pod setup 报CocoaPods was not able to update the `master` repo 错误解决办法

先删除全局的缓存：
$ sudo rm -fr ~/Library/Caches/CocoaPods/
$ sudo rm -fr ~/.cocoapods/repos/master/

还不行的话就把当前 Pods 目录清空：
$ sudo rm -fr Pods/

// 再执行
$ sudo gem install cocoapods

$ pod setup 看看还有没有报错