清单页 https://developer.apple.com/download/more/
Xcode8.3.xip
http://adcdownload.apple.com/Developer_Tools/Xcode_8.3/Xcode_8.3.xip
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AppStore总是更新请求超时，遂，找到一个官方HTTP下载地址：http://adcdownload.apple.com/Developer_Tools/Xcode_7.1/Xcode_7.1.dmg
大小：4.62G