..to avoid rebuilding galleries all the time
because 'version' rc-file target is PHONY.
Instead name what exactly is needed.

Change-Id: Idf3c5a4a5b64a48ae06c46acf24e49f6a1ac2114
Reviewed-on: https://gerrit.libreoffice.org/20407Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Matúš Kukan <matus@libreoffice.org>