Fixes #483: Updating celery to latest fixes issues.
Fixes #483: Updating celery to latest fixes issues.

We were using celery correctly. Our version was just out-dated.

churchlab/millstone,woodymit/millstone_accidental_source,woodymit/millstone_accidental_source,woodymit/millstone,woodymit/millstone_accidental_source,woodymit/millstone,woodymit/millstone_accidental_source,woodymit/millstone,woodymit/millstone,churchlab/millstone,churchlab/millstone,churchlab/millstone