系統升級到Mac OS X EI Capitan后，使用命令：sudo gem install cocoapods，安裝cocoapods，出現以下錯誤：
ERROR:Could not find a valid gem 'cocoapods' (>= 0), here is why:Unable to download data from http://ruby.taobao.org/ - bad response Not Found 404 (http://ruby.taobao.org/latest_specs.4.8.gz)
解決方法：
1. ?gem sources --remove http://ruby.taobao.org/
2. ?gem sources -a https://ruby.taobao.org/
再次嘗試：sudo gem install cocoapods，出現新的錯誤：
ERROR:While executing gem ... (Errno::EPERM)
Operation not permitted - /usr/bin/xcodeproj
解決方法：
sudo gem install -n /usr/local/bin cocoapods
OK!
