CocoaPods [!] Unable to add a so

今天装CocoaPods的时候陷坑一直卡在Setting up CocoaPods master repo，然后等待很久后弹出“[!] Unable to add a source with url https://github.com/CocoaPods/Specs.git named master.”

解决方案如下：
1.进入CocoaPods的目录
cd ~/.cocoapods/repos

2.clone一份代码下来
git clone https://github.com/CocoaPods/Specs.git master

这个问题在github上的讨论链接：
https://github.com/CocoaPods/CocoaPods/issues/4293