* Removed builds for unsupported 3.0 release line
* Added 3.3 release testing
Note that we're trying to make this smarter going forward, just testing against `3@stable` (see https://github.com/silverstripe-labs/silverstripe-travis-support/issues/33)
* Testing on PHP 5.6, reduced variations
Testing every release line against every DB driver and every PHP version tends to increase the complexity of maintaining the builds (more chance of a false negative). It also strains the free resources provided by Travis CI