Build gems for ruby-2.0.0

This PR adds ruby-2.0.0 to the `ruby::all::gem` define, such that it will
compile and install the gem for ruby 2.0.0 I've tested this with the `zeus`
gem, but it might not work for all gems.

I'd appreciate some testing of by anyone who uses the following classes:

 - gds-development
 - git-pulls
 - git-remote-branch
 - github_gem
 - travis
 - vagrant-dns
 - vagrant-vbguest
 - vagrant_gem
 - zeus