sudo apt-get install ruby2.0 ruby2.0-dev libssl-dev make g++
sudo rm /usr/bin/ruby /usr/bin/gem /usr/bin/irb /usr/bin/rdoc /usr/bin/erb sudo ln -s /usr/bin/ruby2.0 /usr/bin/ruby sudo ln -s /usr/bin/gem2.0 /usr/bin/gem sudo ln -s /usr/bin/irb2.0 /usr/bin/irb sudo ln -s /usr/bin/rdoc2.0 /usr/bin/rdoc sudo ln -s /usr/bin/erb2.0 /usr/bin/erb sudo gem update --system sudo gem pristine --all
Source: http://blog.costan.us/2014/04/restoring-ruby-20-on-ubuntu-1404.html