iOS Cocoapods1.8 Failed to open TCP connection to raw.githubusercontent.com:443
Cocoapods 1.7.2 版本开始增加 CDN 支持但默认没有启用，
1.8 版本的发布舍弃了原始完整克隆的 Specs 仓库改用 CDN 服务。
反正pod install的时候报错了
CDN: trunk URL couldn't be downloaded: https://raw.githubusercontent.com/CocoaPods/Specs/master/Specs/a/a/4/Masonry/1.1.0/Masonry.podspec.json, error: Failed to open TCP connection to raw.githubusercontent.com:443 (Connection refused - connect(2) for "raw.githubusercontent.com" port 443)
解决方案一：
在Podfile文件中增加
source "https://github.com/CocoaPods/Specs.git"
