demosite: fix default value of package argument
demosite: fix default value of package argument

* Allows installations that don't use the invenio_demosite.

Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

tiborsimko/invenio-base,tiborsimko/invenio-base,inveniosoftware/invenio-base,inveniosoftware/invenio-base