[TASK] #5176 Update maximum PHP version to 5.6

Change-Id: I854897f3d8225f2cb4a23e991972270c09c1544b
Reviewed-on: http://review.typo3.org/34663
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>