因为一些编译构建问题，我需要降级CocoaPods
过程如下:

卸载当前版本的CocoaPods

sudo gem uninstall cocoapods

下载指定版本的CocoaPods，编译gem包

下载地址https://github.com/CocoaPods/CocoaPods/releases
将源码下载后解压，进入源码目录，编译gem包

gem build cocopods.gemspec

编译产物是 cocopods-版本号.gem

使用本地gem包安装CocoaPods

sudo gem install cocopods-版本号.gem