Upgrade Registrar deps using Python 3.5, not 3.6 (#904)
Upgrade Registrar deps using Python 3.5, not 3.6 (#904)

Registrar still tests and deploys on Python 3.5.
While it's generally 3.6-compatible, sometimes
'make upgrade' PRs will fail in our tests suite if
they are upgraded using Python 3.6, because they pull
in packages that are not 3.5-compatible.

Until we start upgrading to Python 3.6, run the
upgrade job in Python 3.5.
edx/jenkins-job-dsl