在命令行中，我发出：

composer install

输出

Installing dependencies from lock file (including require-dev)
Verifying lock file contents can be installed on current platform.
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. It is recommended that you run `composer update` or `composer update <package name>`.
Your lock file does not contain a compatible set of packages. Please run composer update.

  Problem 1
    - doctrine/cache is locked to version v1.8.0 and an update of this package was not requested.
    - doctrine/cache v1.8.0 requires php ~7.1 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 2
    - doctrine/dbal is locked to version v2.9.2 and an update of this package was not requested.
    - doctrine/dbal v2.9.2 requires php ^7.1 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 3
    - doctrine/event-manager is locked to version v1.0.0 and an update of this package was not requested.
    - doctrine/event-manager v1.0.0 requires php ^7.1 -> your php version (8.0.0) does not satisfy that
requirement.
  Problem 4
    - doctrine/inflector is locked to version v1.3.0 and an update of this package was not requested.
    - doctrine/inflector v1.3.0 requires php ^7.1 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 5
    - maatwebsite/excel is locked to version 3.1.13 and an update of this package was not requested.
    - maatwebsite/excel 3.1.13 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 6
    - markbaker/complex is locked to version 1.4.7 and an update of this package was not requested.
    - markbaker/complex 1.4.7 requires php ^5.6.0|^7.0.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 7
    - markbaker/matrix is locked to version 1.1.4 and an update of this package was not requested.
    - markbaker/matrix 1.1.4 requires php ^5.6.0|^7.0.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 8
    - opis/closure is locked to version 3.2.0 and an update of this package was not requested.
    - opis/closure 3.2.0 requires php ^5.4 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 9
    - phpoffice/phpspreadsheet is locked to version 1.6.0 and an update of this package was not requested.
    - phpoffice/phpspreadsheet 1.6.0 requires ext-gd * -> it is missing from your system. Install or enable PHP's gd extension.
  Problem 10
    - ramsey/uuid is locked to version 3.8.0 and an update of this package was not requested.
    - ramsey/uuid 3.8.0 requires php ^5.4 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 11
    - renatomarinho/laravel-page-speed is locked to version 1.8.10 and an update of this package was not requested.
    - renatomarinho/laravel-page-speed 1.8.10 requires php ^5.6 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 12
    - symfony/psr-http-message-bridge is locked to version v1.2.0 and an update of this package was not
requested.
    - symfony/psr-http-message-bridge v1.2.0 requires php ^7.1 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 13
    - tijsverkoyen/css-to-inline-styles is locked to version 2.2.1 and an update of this package was not requested.
    - tijsverkoyen/css-to-inline-styles 2.2.1 requires php ^5.5 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 14
    - zendframework/zend-diactoros is locked to version 1.8.6 and an update of this package was not requested.
    - zendframework/zend-diactoros 1.8.6 requires php ^5.6 || ^7.0 -> your php version (8.0.0) does not
satisfy that requirement.
  Problem 15
    - composer/semver is locked to version 1.5.0 and an update of this package was not requested.
    - composer/semver 1.5.0 requires php ^5.3.2 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 16
    - composer/xdebug-handler is locked to version 1.3.2 and an update of this package was not requested.
    - composer/xdebug-handler 1.3.2 requires php ^5.3.2 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 17
    - doctrine/annotations is locked to version v1.6.1 and an update of this package was not requested.
    - doctrine/annotations v1.6.1 requires php ^7.1 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 18
    - doctrine/instantiator is locked to version 1.2.0 and an update of this package was not requested.
    - doctrine/instantiator 1.2.0 requires php ^7.1 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 19
    - facebook/webdriver is locked to version 1.6.0 and an update of this package was not requested.
    - facebook/webdriver 1.6.0 requires php ^5.6 || ~7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 20
    - filp/whoops is locked to version 2.3.1 and an update of this package was not requested.
    - filp/whoops 2.3.1 requires php ^5.5.9 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 21
    - friendsofphp/php-cs-fixer is locked to version v2.15.0 and an update of this package was not requested.
    - friendsofphp/php-cs-fixer v2.15.0 requires php ^5.6 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 22
    - fzaninotto/faker is locked to version v1.8.0 and an update of this package was not requested.
    - fzaninotto/faker v1.8.0 requires php ^5.3.3 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 23
    - hamcrest/hamcrest-php is locked to version v2.0.0 and an update of this package was not requested.    - hamcrest/hamcrest-php v2.0.0 requires php ^5.3|^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 24
    - myclabs/deep-copy is locked to version 1.9.1 and an update of this package was not requested.
    - myclabs/deep-copy 1.9.1 requires php ^7.1 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 25
    - phar-io/manifest is locked to version 1.0.1 and an update of this package was not requested.
    - phar-io/manifest 1.0.1 requires php ^5.6 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 26
    - phar-io/version is locked to version 1.0.1 and an update of this package was not requested.
    - phar-io/version 1.0.1 requires php ^5.6 || ^7.0 -> your php version (8.0.0) does not satisfy that
requirement.
  Problem 27
    - php-cs-fixer/diff is locked to version v1.3.0 and an update of this package was not requested.
    - php-cs-fixer/diff v1.3.0 requires php ^5.6 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 28
    - phpdocumentor/reflection-docblock is locked to version 4.3.1 and an update of this package was not requested.
    - phpdocumentor/reflection-docblock 4.3.1 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 29
    - phpdocumentor/type-resolver is locked to version 0.4.0 and an update of this package was not requested.
    - phpdocumentor/type-resolver 0.4.0 requires php ^5.5 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 30
    - phpspec/prophecy is locked to version 1.8.0 and an update of this package was not requested.
    - phpspec/prophecy 1.8.0 requires php ^5.3|^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 31
    - phpunit/php-code-coverage is locked to version 5.3.2 and an update of this package was not requested.
    - phpunit/php-code-coverage 5.3.2 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 32
    - phpunit/php-timer is locked to version 1.0.9 and an update of this package was not requested.
    - phpunit/php-timer 1.0.9 requires php ^5.3.3 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 33
    - phpunit/php-token-stream is locked to version 2.0.2 and an update of this package was not requested.
    - phpunit/php-token-stream 2.0.2 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 34
    - phpunit/phpunit is locked to version 6.5.14 and an update of this package was not requested.
    - phpunit/phpunit 6.5.14 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 35
    - phpunit/phpunit-mock-objects is locked to version 5.0.10 and an update of this package was not requested.
    - phpunit/phpunit-mock-objects 5.0.10 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 36
    - sebastian/code-unit-reverse-lookup is locked to version 1.0.1 and an update of this package was not requested.
    - sebastian/code-unit-reverse-lookup 1.0.1 requires php ^5.6 || ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 37
    - sebastian/comparator is locked to version 2.1.3 and an update of this package was not requested.
    - sebastian/comparator 2.1.3 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 38
    - sebastian/diff is locked to version 2.0.1 and an update of this package was not requested.
    - sebastian/diff 2.0.1 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 39
    - sebastian/environment is locked to version 3.1.0 and an update of this package was not requested.
    - sebastian/environment 3.1.0 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 40
    - sebastian/exporter is locked to version 3.1.0 and an update of this package was not requested.
    - sebastian/exporter 3.1.0 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 41
    - sebastian/global-state is locked to version 2.0.0 and an update of this package was not requested.    - sebastian/global-state 2.0.0 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 42
    - sebastian/object-enumerator is locked to version 3.0.3 and an update of this package was not requested.
    - sebastian/object-enumerator 3.0.3 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 43
    - sebastian/object-reflector is locked to version 1.1.1 and an update of this package was not requested.
    - sebastian/object-reflector 1.1.1 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 44
    - sebastian/recursion-context is locked to version 3.0.0 and an update of this package was not requested.
    - sebastian/recursion-context 3.0.0 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 45
    - theseer/tokenizer is locked to version 1.1.2 and an update of this package was not requested.
    - theseer/tokenizer 1.1.2 requires php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
  Problem 46
    - webmozart/assert is locked to version 1.4.0 and an update of this package was not requested.
    - webmozart/assert 1.4.0 requires php ^5.3.3 || ^7.0 -> your php version (8.0.0) does not satisfy th  Problem 47
    - doctrine/inflector v1.3.0 requires php ^7.1 -> your php version (8.0.0) does not satisfy that requirement.
    - laravel/framework v5.5.45 requires doctrine/inflector ~1.1 -> satisfiable by doctrine/inflector[v1.3.0].
    - laravel/framework is locked to version v5.5.45 and an update of this package was not requested.

To enable extensions, verify that they are enabled in your .ini files:
    - C:\xampp\php\php.ini
You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

和：

composer update

输出

Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - maatwebsite/excel 3.1.26 requires phpoffice/phpspreadsheet ^1.15 -> satisfiable by phpoffice/phpspreadsheet[1.15.0, 1.16.0].
    - maatwebsite/excel[3.1.0, ..., 3.1.25] require php ^7.0 -> your php version (8.0.0) does not satisfy that requirement.
    - phpoffice/phpspreadsheet[1.15.0, ..., 1.16.0] require ext-gd * -> it is missing from your system.
Install or enable PHP's gd extension.
    - Root composer.json requires maatwebsite/excel ^3.1 -> satisfiable by maatwebsite/excel[3.1.0, ..., 3.1.26].

To enable extensions, verify that they are enabled in your .ini files:
    - C:\xampp\php\php.ini
You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.

我该如何解决这个问题？