[TASK] Raise version to 1.3.1-dev

Change-Id: I25748138a1b77660e393b9b505efcef848943014
Reviewed-on: http://review.typo3.org/32366
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>