Pin the CircleCI mongo docker image to 3.2-jessie
Pin the CircleCI mongo docker image to 3.2-jessie

Match the version of mongo used in production to fix the
'Use of SCRAM-SHA-256 requires undigested passwords' errors
from pymongo seen during CI runs. The errors were due to
the breaking changes in the latest version 4.0.

open-craft/opencraft,open-craft/opencraft,open-craft/opencraft,open-craft/opencraft,open-craft/opencraft