Reduce the number of builds performed by Travis CI to (I think) the essentials.
Reduce the number of builds performed by Travis CI to (I think) the essentials.

Travis CI (should) perform the following builds
- PHP 5.4 / Symfony 2.3
- PHP 5.5 / Symfony 2.3
- PHP 5.4 / Symfony 2.6
- PHP 5.6 / Symfony 2.7@dev (allowed failure)

dankempster/axstrad-doctrine-extensions-bundle