原文地址：https://my.oschina.net/jjtm/blog/492083
pod update出现：
[!] Unable to add a source with url `https://github.com/CocoaPods/Specs.git` named `master-1`.
You can try adding it manually in `~/.cocoapods/repos` or via `pod repo add`.
这样的提示。
解决办法：由于装了多个Xcode，在终端输入：sudo xcode-select -switch /Applications/Xcode8.0.app
