Mac上有两个Xcode，一个是正式版，另一个安装的测试版，pod install的时候发现报错，找不到对应的Xcode，错误如下：
Setting up CocoaPods master repo
$ /usr/bin/git remote set-url origin https://github.com/CocoaPods/Specs.git
xcrun: error: active developer path ("/Applications/Xcode.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`)
[!] Failed: /usr/bin/git remote set-url origin https://github.com/CocoaPods/Specs.git
$ /usr/bin/git checkout master
xcrun: error: active developer path ("/Applications/Xcode.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`)
[!] Failed: /usr/bin/git checkout master
[!] Unable to add a source with url `https://github.com/CocoaPods/Specs.git` named `master-1`.
(The `master` repo is not a git repo.)
You can try adding it manually in `~/.cocoapods/repos` or via `pod repo add`.
经百度查找，了解如下可以解决此问题：
sudo xcode-select --switch /Applications/Xcode.app
