[TASK] Raise PHP requirement to 5.5

Releases: 2.0.0
Change-Id: I1d6c38d6c348c286e2718fe3e4b181adcc089254
Reviewed-on: http://review.typo3.org/34819
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>