Update Travis config and remove librarian-puppet

* Switch to installing modules from Forge with puppetlabs_spec_helper which recently introduced support. Brings things closed in line with the Puppetlabs module setup.
* Extend the Travis build matrix
  * Add ruby 2.1.0
  * Add ruby 1.8.7 testing with both Puppet 2.7.x and Puppet 3.x (given module policy is YMMV with Ruby 1.8.7 these are allowed failures, meaning you still get the results from Travis but the overall build won't fail)
  * Enable Travis fast finish for quicker feedback on failing builds
  * Simply Travis matrix to make it easier to understand which combinations of Puppet/Ruby are being tested.
* Fix a couple minor issues from updating the tested module dependencies (librarian-puppet had them locked to older versions).