CocoaPods 最新源
https://www.jianshu.com/p/9b5a25dbcaa7
https://gems.ruby-china.com/
https://blog.cocoapods.org/CocoaPods-1.7.2/
source 'https://github.com/artsy/Specs.git'
- source 'https://github.com/CocoaPods/Specs.git'
+ source 'https://cdn.cocoapods.org/'