Require 'active_support' before any of the extensions

Without this we would get random errors on travis-ci and it is just
coincidence we're not getting them locally, too. According to this
https://github.com/rails/rails/issues/14664 it is always required
to load 'active_support' before any of its components get loaded.
Merge pull request #57 from triAGENS/correctly-load-activesupport

Require 'active_support' before any of the extensions
We want to build against the latest Ruby as well
Use latest Ruby (2.1.2) as ruby-version