Bug 2075120 - Bump rumdl to 0.1.96 since 0.1.91 is no longer on PyPI r=dao, a=dsmith DONTBUILD
rumdl 0.1.91 was removed from PyPI upstream, so the lint and python-test virtualenvs can no longer be created. 0.1.96 is the nearest published release and reports no new errors in-tree. Differential Revision: https://phabricator.services.mozilla.com/D328750