正常cocoapods更新版本的命令
sudo gem install cocoapods
但是呢，经常都会遇到权限不足的情况，所以改成下面的命令
sudo gem install -n /usr/local/bin cocoapods
还有如果你想指定安装cocoapods 版本号，只需要在命令的最后面 加上对应的版本号就可以了
sudo gem install -n /usr/local/bin cocoapods -v 1.8.3
会安装当然需要会卸载，卸载的方法如下
1.卸载老版本cocopods
$ sudo gem uninstall cocoapods
2.查看本地安装过的cocopods相关东西
$ gem list --local | grep cocoapods
显示如下:
cocoapods (1.0.1)
cocoapods-core (1.0.1)
cocoapods-deintegrate (1.0.1)
cocoapods-downloader (1.1.1)
cocoapods-plugins (1.0.0)
cocoapods-search (1.0.0)
cocoapods-stats (1.0.0)
cocoapods-trunk (1.0.0)
cocoapods-try (1.1.0)
然后使用命令逐个删除
$ sudo gem uninstall cocoapods-core
$ sudo gem uninstall cocoapods-deintegrate
如果怕删不干净有残留的话可以找到 .cocopods 文件（隐藏文件）删掉就好
