Revert "[BUGFIX] Fix broken link to security resources page on typo3.org"

This URL change on typo3.org had bigger impact and was reverted.
Revert this back here as well.

This reverts commit d92f3ef2.

Change-Id: Ic75ed47edcca9bfff3af6595af02bc81fe6a14c0
Reviewed-on: http://review.typo3.org/42989


Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>