Now testing puppet 3.6, dropping 3.1

At first I added 3.6, here is that matrix:
https://travis-ci.org/solarkennedy/puppet-bios/builds/29159096

I agree that it is getting pretty big.
The tricky thing about puppet, is that it is pretty prolific, as there is a lot of inertia against old platforms.
There are plenty of people and distros with ruby 1.8.7, still using puppet from their package manager.
http://docs.puppetlabs.com/guides/platforms.html#ruby-versions


So I made a conservative removal of 3.1, to keep the matrix size about the same with this PR
https://travis-ci.org/solarkennedy/puppet-bios/builds/29159640