更新gem

$ sudo gem update -n /usr/local/bin --system

更新Ruby源

$ gem sources --add https://gems.ruby-china.com/ --remove https://rubygems.org/

检查Ruby源

$ gem sources -l
https://gems.ruby-china.com

确保只有gems.ruby-china.com

如果安装了多个Xcode，用以下命令选择

$ sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer

安装Cocoapods

 $ sudo gem install -n /usr/local/bin cocoapods

安装指定版本的Cocoapods

$ sudo gem install -n /usr/local/bin cocoapods -v 1.5.3