Обновите версию Ruby
rvm list known
rvm install ruby@latest
ruby -v
## If it still shows you ruby 2.0., run rvm use ruby-X.X.X --default.
Undefined
rvm list known
rvm install ruby@latest
ruby -v
## If it still shows you ruby 2.0., run rvm use ruby-X.X.X --default.# Use RVM to install ruby
# https://rvm.io/
# then run this command
# rvm install ruby@latest