Use the new build env on Travis

more ram, more cpu, better network

http://docs.travis-ci.com/user/workers/container-based-infrastructure/

more docs coming soon
Merge pull request #511 from joshk/patch-2

Use the new build env on Travis
Tests adjustments:

* Rails 4.2.0.beta4 and Arel 6 are not playing well together right now
* cache bundle in Travis CI
* Factories rearrangement