https://github.com/xiaolai/xiaolai.github.io/blob/master/2016/06/16/makecs-basic-dev-env-settup/index.html “安装 rvm 与 Ruby 2.3.1”章节 建议在安装前，添加一项，查看rvm上可用的Ruby版本： ‘rvm list known | head -15’
