iOS Cocoapods1.8 Failed to open TCP connection to raw.githubusercontent.com:443
Cocoapods 1.7.2 版本開始增加 CDN 支持但默認沒有啟用，
1.8 版本的發布舍棄了原始完整克隆的 Specs 倉庫改用 CDN 服務。
反正pod install的時候報錯了
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)
解決方案一：
在Podfile文件中增加
source "https://github.com/CocoaPods/Specs.git"
