[ticket/11324] PHP 5.5 is in RC stage. No longer allow failure on travis.

PHPBB3-11324
Merge pull request #1396 from bantu/ticket/11324

[ticket/11324] PHP 5.5 is in RC state. No longer allow failure on travis...
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [ticket/11324] PHP 5.5 is in RC stage. No longer allow failure on travis.