启动rails服务器时，我遇到了以下错误：
未捕获的异常：nil：NilClass的方法"formatter"未定义
还有另一个StackOverflow问题NoMethodError on Rails Server，建议将require './app'添加到config.ru文件中，但该解决方案对我不起作用（导致错误）。
我还尝试在我的gemfile中添加logger gem，因为我最近卸载了所有gem来解决这个问题。
Your bundle is locked to rake (12.0.0), but that version could not be found in any of the sources listed in your Gemfile.
确切的控制台输出如下所示：

/home/daniel/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.5/lib/rails/commands/server.rb:142:in `log_to_stdout'
	/home/daniel/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.5/lib/rails/commands/server.rb:78:in `start'
	/home/daniel/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:80:in `block in server'
	/home/daniel/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:75:in `tap'
	/home/daniel/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:75:in `server'
	/home/daniel/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
	/home/daniel/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/railties-4.2.5/lib/rails/commands.rb:17:in `<top (required)>'
	/home/daniel/Data/RubyOnRails/YoutubeBlog/bin/rails:4:in `require'
	/home/daniel/Data/RubyOnRails/YoutubeBlog/bin/rails:4:in `<top (required)>'
Exiting

Config.ru

# This file is used by Rack-based servers to start the application.

require ::File.expand_path('../config/environment', __FILE__)
run Rails.application

我删除了宝石文件，运行bundle install和bundle update没有解决问题。（谢谢你的建议）。
任何帮助都将不胜感激。|