I have gone about the recommended way of installing a new version of Ruby on Mac OS X: Homebrew, and rvm. I ran rbenv to install Ruby 2.3.3, and selected it as the preferred version by using "rbenv global 2.3.3". The problem I am having is that there is currently a 2.0.0 version installed at /usr/bin/ruby, and for some crazy reason I am unable to remove it.
$ rbenv global
2.3.3
$ which ruby
/usr/bin/ruby
$ ruby -v
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]
$ ~/.rbenv/versions/2.3.3/bin/ruby -v
ruby 2.3.3p222 (2016-11-21 revision 56859) [x86_64-darwin16]
sudo rm -rf /usr/bin/ruby
Password:
rm: /usr/bin/ruby: Operation not permitted
Argh!! Please help.