xcode 更新后，pod install 失败

错误信息：

[!] 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`.

解决方法：
1、执行命令 $ sudo xcode-select -switch /Applications/Xcode.app

2、输入密码

3、重新执行 $ pod install