PHPUnit as a dev dependency

See #64.

Drop support for non-LTS versions of Symfony

Merge pull request #61 from pamil/update-constraints

Update Travis matrix build & bump up Composer dependencies

v0.7.6: Merge pull request #55 from Soullivaneuh/sf3

Allow Symfony 3

v0.7.5: Merge pull request #50 from xabbuh/issue-49

swap actual and expected value in error message