Pod 出错 xcrun: error: active developer path

xcrun: error: active developer path ("/Applications/Xcode7.app/Contents/Developer") does not exist, use `xcode-select --switch path/to/Xcode.app` to specify the Xcode that you wish to use for command line developer tools (or see `man xcode-select`)

Creating shallow clone of spec repo `master-1` from `https://github.com/CocoaPods/Specs.git`

[!] 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`.

出现这个错误 多数是因为 Xcode更新之后 Command Line Tools 没有选择 所以找不到Xcode