- Updating Python Requirements
- Fix cache key generation to use class name and module

This was stringifying the class object directly, resulting in cache keys
like `:1:<class 'xblock_django.models.XBlockConfiguration'>.xblock_django.api.deprecated_xblocks`
which then cause breakage when Django 2.2.13 validates the keys.

Co-authored-by: edX requirements bot <testeng+edx-requirements-bot@edx.org>