[BUGFIX] Use correct class name used to render tstamp

Resolves: #6376
Releases: master
Change-Id: I689cc839d00128349ec29c1f8da10233d9e4f1a3
Reviewed-on: http://review.typo3.org/35289
Reviewed-by: Fabien Udriot <fabien.udriot@ecodev.ch>
Tested-by: Fabien Udriot <fabien.udriot@ecodev.ch>