title: Rails can't run：`require': incompatible library version
body: <p>I use rvm for ruby version management,
  but rails can't run when I execute 'rails s'.<br>
  I reinstall rvm,and I also reinstall gems still problem.<br>
  I'm desperate and need your help!<br>
  console log:
  <code>
  /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/mysql2-0.3.21/lib/mysql2.rb:31:in `require': incompatible library version - /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/mysql2-0.3.21/lib/mysql2/mysql2.bundle (fatal)
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/mysql2-0.3.21/lib/mysql2.rb:31:in `&lt;top (required)&gt;'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/bundler-1.12.5/lib/bundler/runtime.rb:86:in `require'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/bundler-1.12.5/lib/bundler/runtime.rb:86:in `block (2 levels) in require'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/bundler-1.12.5/lib/bundler/runtime.rb:81:in `each'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/bundler-1.12.5/lib/bundler/runtime.rb:81:in `block in require'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/bundler-1.12.5/lib/bundler/runtime.rb:70:in `each'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/bundler-1.12.5/lib/bundler/runtime.rb:70:in `require'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/bundler-1.12.5/lib/bundler.rb:102:in `require'
      from /Users/brucewzp/develop/rubydev/lofi/config/application.rb:7:in `&lt;top (required)&gt;'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:78:in `require'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:78:in `block in server'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:75:in `tap'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:75:in `server'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0@global/gems/railties-4.2.6/lib/rails/commands.rb:17:in `&lt;top (required)&gt;'
      from /Users/brucewzp/develop/rubydev/lofi/bin/rails:9:in `require'
      from /Users/brucewzp/develop/rubydev/lofi/bin/rails:9:in `&lt;top (required)&gt;'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/spring-1.7.1/lib/spring/client/rails.rb:28:in `load'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/spring-1.7.1/lib/spring/client/rails.rb:28:in `call'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/spring-1.7.1/lib/spring/client/command.rb:7:in `call'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/spring-1.7.1/lib/spring/client.rb:30:in `run'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/spring-1.7.1/bin/spring:49:in `&lt;top (required)&gt;'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/spring-1.7.1/lib/spring/binstub.rb:11:in `load'
      from /Users/brucewzp/.rvm/gems/ruby-2.3.0/gems/spring-1.7.1/lib/spring/binstub.rb:11:in `&lt;top (required)&gt;'
      from /Users/brucewzp/develop/rubydev/lofi/bin/spring:13:in `require'
      from /Users/brucewzp/develop/rubydev/lofi/bin/spring:13:in `&lt;top (required)&gt;'
      from bin/rails:3:in `load'
      from bin/rails:3:in `&lt;main&gt;'
  </code></p>