A new django-multiselectfield recently came out, and despite it being a

micro version bump and listing Python 2.7 compatibility, it makes use of

Python 3 type hints. This breaks older builds.
Supported releases of Review Board are not affected by this, but in an

effort to keep CI working and to avoid surprises if we ever need to

supply an older build to a customer, we're now capping this dependency

to an explicit 0.1.12 release.

Tested a new environment and verified I got the 0.1.12 release.