Use master branch of cumulus for docker
Use master branch of cumulus for docker

The master branch of cumulus was recently upgraded to use
girder 3. Use the master branch of cumulus instead of the
migration branch.

Signed-off-by: Patrick Avery <743342299f279e7a8c3ff5eb40671fce3e95f13a@kitware.com>

OpenChemistry/mongochemserver