This is a common problem when you first time install a new version of ruby. To fix this problem please follow below steps:
Set up the PATH variable for the installed ruby executable
(Suppose the installed ruby is ruby-2.1.5):
gem install bundler
(if bundler is not installed)
rvm use ruby-2.1.5 --default
(–default is optional).
This will fix your problem.
Hope it helps 🙂