[BUGFIX] Rename directory hook -> Hook

This fixes the error that hooks cannot be found when
the webserver is running on a case sensitive filesystem.

Change-Id: I0758d662d34b337b54931cde8346328d5d298448
Issue: #63936
Resolves: #63936
Reviewed-on: http://review.typo3.org/35519
Reviewed-by: Thomas Löffler <loeffler@spooner-web.de>
Tested-by: Thomas Löffler <loeffler@spooner-web.de>