Improve the PHPunit config
Improve the PHPunit config

- Test on PHP 5.6, PHP 7 and HHVM
- use the faster docker-based infrastructure
- keep the composer cache between builds
- test on lowest version of dependencies
- upload the code coverage to scrutinizer

Incenteev/translation-checker-bundle,Incenteev/IncenteevTranslationCheckerBundle,Incenteev/translation-checker-bundle,Incenteev/IncenteevTranslationCheckerBundle