(FACT-653) Cherry-pick lost update on supported Ruby versions back into master

This commit cherry-picks an update on Facter's officially supported Ruby
versions back into master, which was lost during the facter-2 / master merge.

Original commit (fbeaca9):
(#22857) officially support ruby 2.0

To corespond with puppet >= 3.2 Ruby 2.0 support:
    http://docs.puppetlabs.com/puppet/3/reference/release_notes.html#ruby-20-support
(FACT-653) Doc update for supported Ruby Version cherry-pick

Original commit (6caf1ce4):
(#22857) Note that ruby 2.0.0 should be at least p195.
Merge pull request #761 from whopper/ruby2-cherrypick

(FACT-653) Cherry-pick lost update on supported Ruby versions back into master