Migration: add nailgun compat fix to fits cmd
Migration: add nailgun compat fix to fits cmd

Make sure that the command works when Nailgun's binary is called `ng`
and `nailgun-ng`.

artefactual/archivematica-fpr-admin,artefactual/archivematica-fpr-admin,artefactual/archivematica-fpr-admin,artefactual/archivematica-fpr-admin