coreapi dependency - issues with Python 3.9

[cristianoccazinsp]

site-packages//itypes.py:2: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3,and in 3.9 it will stop working
  from collections import Mapping, Sequence

itypes: Required-by: coreapi coreapi: Required-by: drf-yasg

Looks like both itypes and coreapi repos are archived, can you guys vendor w/e requirements are from there and bump the version to support python 3.9?

Thanks.

[johnthagen]

Duplicate of #389