CentOS 升级 Ruby版本

# gem update --system
Updating rubygems-update
Fetching: rubygems-update-3.0.3.gem (100%)
ERROR:  Error installing rubygems-update:
	rubygems-update requires Ruby version >= 2.3.0.
ERROR:  While executing gem ... (NoMethodError)
    undefined method `version' for nil:NilClass

# gpg2 --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB
# \curl -sSL https://get.rvm.io | bash -s stable
# source /etc/profile.d/rvm.sh
# rvm requirements
# rvm install ruby-head