openedxstats Dependencies Support for Django 2.2

Versions in openedxstats already support Django 2.2

• dj-database-url

• django-bootstrap3

• django-datetime-widget (https://openedx.atlassian.net/browse/BOM-1345)

• django-dotenv (doesn’t actually depend on Django)

• django-filter

• django-model-utils

• djangorestframework

• model_mommy

• whitenoise

Haven't been tested with Django 2.2 upstream

• django-jenkins (has issues with recent pylint and coverage also)