cocoapad 错误解决

[!] Unable to add a source with url `https://github.com/CocoaPods/Specs.git` named `master`.

You can try adding it manually in `~/.cocoapods/repos` or via `pod repo add`.

我尝试按提示的方法 

pod repo add master https://github.com/CocoaPods/Specs.git

然而还是有错.. 

[!] /usr/bin/git clone http://git.oschina.net/akuandev/Specs.git master

xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun

最后的解决方法： sudo xcode-select -switch /Applications/Xcode.app/Contents/Developers