CDN: trunk URL couldn't be downl

CDN: trunk URL couldn't be downloaded: https://raw.githubusercontent.com/CocoaPods/Specs/master/Specs/0/f/b/MJRefresh/3.3.1/MJRefresh.podspec.json, error: Failed to open TCP connection to raw.githubusercontent.com:443 (Connection refused - connect(2) for "raw.githubusercontent.com" port 443)

解决方式是 在Podfile文件中添加

source 'https://github.com/CocoaPods/Specs.git'