If ruby is installed with RVM, it should be loaded when user session is startup.
By default RVM put loading script in bash_profile. There are two way to make it work:
1. In Preference of Gnome Terminal, enable “Run command as a login shell”
2. If concerned about security, we can copy command from “bash_profile” and put it in “bashrc”
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM into a shell session *as a function*