[TASK] Bump the version number to 0.7.81.

Change-Id: Ia4c6e5c48af9b6ce2777b97a4f620a70afc7c3c5
Reviewed-on: http://review.typo3.org/32589
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>