Added new version of puppet/ruby to test against, and use https for rubygems

Now that 3.5 is out, I would like to test against it. Also, Ruby 2.1.0 is supported.
I'm pretty sure I've got the matrix right that matches what Puppetlabs supports:
http://docs.puppetlabs.com/guides/platforms.html#ruby-versions

I always use your skeleton's .travis as a reference, as it is is always up to date, so I'm happy to PR to update it!

Also, https for rubygems for mitm protection?