使用gem安装cocoapods sudo gem install cocoapod 此时报错： Unable to resolve dependencies: cocoapods requires cocoapods-core
先更新gem然后重新开始
sudo gem update --system
sudo gem install cocoapods
//出现 Operation not permitted - /usr/bin/xcodeproj
//使用下面的命令就可以解决
sudo gem install -n /usr/local/bin cocoapods
