mac rvm 升级 ruby 安装cocoapod 指定版本
安装 rvm
$ curl -L get.rvm.io | bash -s stable
$ source ~/.bashrc
$ source ~/.bash_profile
$ rvm list known
$ rvm install 2.5.1
$ sudo gem install cocoapods -v 1.5.3
安装 rvm
$ curl -L get.rvm.io | bash -s stable
$ source ~/.bashrc
$ source ~/.bash_profile
$ rvm list known
$ rvm install 2.5.1
$ sudo gem install cocoapods -v 1.5.3