OS X升级到10.10之后使用pod出现问题的解决方法

错误提示：
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in require': cannot load such file -- xcodeproj/prebuilt/universal.x86_64-darwin14-2.0.0/xcodeproj_ext (LoadError) from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:inrequire'
from /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/lib/xcodeproj/ext.rb:6:in rescue in <top (required)>' from /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/lib/xcodeproj/ext.rb:3:in<top (required)>'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in require' from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:inrequire'
from /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/lib/xcodeproj.rb:30:in <top (required)>' from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:inrequire'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in require' from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.33.1/lib/cocoapods.rb:2:in<top (required)>'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in require' from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:inrequire'
from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.33.1/bin/pod:32:in <top (required)>' from /usr/bin/pod:23:inload'
from /usr/bin/pod:23:in `<main>'

解决方法：

1. 打开 Xcode
2. 进入 Preferences
3. 点击Locations选项
4. 将 Command Line Tools 版本变成 Xcode
5. 卸载 cocoapods，在终端中输入

sudo gem uninstall cocoapods

6.安装xcodeproj，在终端中输入
sudo gem install xcodeproj

7.安装cocoapods，在终端中输入
sudo gem install cocoapods

8.测试pod是否安装成功，在终端中输入
pod --version