centos 使用 jekyll 安装ruby 使用 gem 命令

参考：https://www.digitalocean.com/community/articles/how-to-install-ruby-2-1-0-on-centos-6-5-using-rvm

http://jekyllrb.com/

install rvm

install ruby

use gem

1. update RVM: rvm get head
2. read and follow instructions: rvm requirements
3. reinstall ruby: rvm reinstall 1.9.2