curl -fsSL https://raw.githubusercontent.com/supermarin/Alcatraz/deploy/Scripts/install.sh | sh
Failed to connect to github-cloud.s3.amazonaws.com
总结来说，当源都不行时，找别的思路。到官网或github上看看说明。
重新打开Xcode > Window > Package Manager
原文：http://www.cnblogs.com/SimonGao/p/4972363.html