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/'