[ticket/12188] Add php 5.6 to travis enviroments

PHPBB3-12188
Merge remote-tracking branch 'github-nickvergessen/ticket/12188' into develop-olympus

* github-nickvergessen/ticket/12188:
  [ticket/12188] Add php 5.6 to travis enviroments
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [ticket/12188] Add php 5.6 to travis enviroments

Conflicts:
	.travis.yml