由于先安装 Appium 后再安装 Xcode 获取不到 Xcode 版本，
Could not determine Xcode version: Could not get Xcode version. /Library/Developer/Info.plist does not exist on disk.

解决方案：卸载 Appium，重新安装
npm uninstall -g appium
npm install -g appium@1.6.3