[TASK] #5176 Update maximum PHP version to 5.6

Change-Id: I6ecedf92de33c2bf07cfc6d28823cf991f3145de
Reviewed-on: http://review.typo3.org/34662
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>