Celery 5.3 alpha is now up on PyPI, and this is not compatible with

Python 3.6. Technically, Celery 5.2.x wasn't compatible either, but it

did seem to run.
As Celery is apparently not using semantic versioning, we can't trust

that 5.x will remain compatible. We're now capping the version to the

5.1.x range for Python 3.6, and 5.2.x for newer versions.
It also bumps up the minimum version for each range.

Successfully installed packages on each version of Python and ran

unit tests for the extension and worker.