install ruby 2.1.0 on ubuntu

1: install curl

$ sudo apt-get install curl

2: install rvm and check requirements

$ curl -L get.rvm.io | bash -s stable

$ source ~/.rvm/scripts/rvm

$ rvm requirements

3: install ruby

$ rvm install 2.1.0

4. edit .bash.rc if you want use ruby in non log-in terminal

[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM into a shell session *as a function*