[TASK] Adjust Travis to new requirements for version 7

Drop the testing for PHP versions below 5.5

Resolves: #61969
Releases: master
Change-Id: I393a463e0ed1648b58c05c1691a65551e4d4bbab
Reviewed-on: http://review.typo3.org/33068
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>