[TASK] #5176 Update maximum PHP version to 5.6

Change-Id: I05c548fe33e7165dc39a16676c2f19695a53a4a3
Reviewed-on: http://review.typo3.org/34664
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>