Travis won't respect the matrix unless you pass the full env

https://travis-ci.org/craigwatson/puppet-vmwaretools/builds/35996082

^^ Builds Puppet 3.2, 3.3 and 3.4 against Ruby 2.1.0 even though it's in the exclude matrix

https://travis-ci.org/craigwatson/puppet-vmwaretools/builds/35996295

^^ Respects the matrix and uses Ruby 2.0.0 for Puppet 3.2, 3.3 and 3.4