环境：OSX EI 10.11.1
昨天切换gem源后，招待pod安装没有任何问题，也可以正常用
$ gem sources --add https://ruby.taobao.org/ --remove https://rubygems.org/
$ sudo gem install cocoapods
今天再使用的时候，在一个项目下执行pod install时半天死活没反应，无奈就ctrl+c了强制退出了。然后再执行的时候就出现错误：
Library/Ruby/Site/2.0.0/rubygems/dependency.rb:318:in `to_specs': Could not find 'cocoapods' (>= 0) among 33 total gem(s) (Gem::LoadError)
Checked in 'GEM_PATH=/Users/xianlong/.gem/ruby/2.0.0:/Library/Ruby/Gems/2.0.0:/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/gems/2.0.0', execute `gem env` for more information
from /Library/Ruby/Site/2.0.0/rubygems/dependency.rb:327:in `to_spec'
from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_gem.rb:64:in `gem'
from /usr/local/bin/pod:22:in `<main>'
分析可能是因为强制退出程序导致的配置被损坏。于是把pod卸载，重新安装后就ok了。
卸载Pod:
step1:
which pod: 查看pod命令所在路径,比如为/usr/local/bin/pod，然后执行 rm -rf /usr/local/bin/pod 将pod命令移除
step2:
执行gem list | grep cocoapods 查看所有与cocoapods相关的已安装的组件，然后挨个卸载
我这里的执行结果是：
cocoapods-core (0.39.0)
cocoapods-downloader (0.9.3)
cocoapods-plugins (0.4.2)
cocoapods-search (0.1.0)
cocoapods-stats (0.6.2)
cocoapods-trunk (0.6.4)
cocoapods-try (0.5.1)
然后我就挨个执行：
gem uninstall cocoapods-core
gem uninstall cocoapods-downloader
gem uninstall cocoapods-plugins
gem uninstall cocoapods-search
gem uninstall cocoapods-stats
gem uninstall cocoapods-trunk
gem uninstall cocoapods-try
step3: 重新安装pod
执行sudo gem install cocoapods， 提示出错：While executing gem ... (Errno::EPERM) Operation not permitted - /usr/bin/pod
在命令中指定安装到/usr/bin/pods下即可正常安装成功：
sudo gem install -n /usr/local/bin cocoapods
安装成功，
step4: 查看新安装的pod版本：
pod --version
0.39.0
