Convert puppet version requirements to rubygems format

Checks puppet requirement to see if it is the equivalent of pessimistic (`1.2.x`) or a range (`>=3.0.0 <4.0.0`) and converts them to their respective rubygems requirement (`~> 1.2` and `['>= 3.0.0', '<4.0.0']` respectively).

Addresses issue reported in #82 and #85.  Any feedback would be appreciated.