Celery 5.1.x (required for Python 3.6) depends on kombu>=5.1.0,<6.0.

The problem is that they've dropped Python 3.6 support in kombu 5.2,

meaning that anyone trying to install this range of Celery versions will

end up with a broken environment.
We try to help them out (and help our CI out) by capping the version

range of kombu so that only versions compatible with Python 3.6 will

install.

Installed packages on Python 3.6 and verified I got the right version

of kombu (and that it removed the incompatible version).
Unclear at this stage if there are other bad dependency ranges that

will have to be capped.