Update .travis.yml to follow newer puppets

Borrowing heavily from
https://github.com/garethr/puppet-module-skeleton/blob/master/skeleton/.travis.yml
as of today, track more versions of puppet.
I don't care about puppet 2.7 anymore.  Sorry y'all
Frob Gemfile to fix outstanding error

Taken wholly from garethr/puppet-module-skeleton

I have no idea why this worked before?  I'm bumping the default puppet
version, that's ok.
Add a :test task

Also disable a puppet-lint error that I can't figure out.  What could go
wrong here?
Merge pull request #4 from BillWeiss/bump-puppet-and-ruby-vers

Bump puppet and ruby vers