Upgrade to Django 3.1

[johanneswilm]

No description provided.

[doughnet]

Awesome. Wonder why it isn't being merged!

[krzysztof-adamski]

How long will we waiting for merge ? But this is not enough. Problem will be in python 3.12
`
try:
from collections import Iterable
except Exception:
from collections.abc import Iterable

try:
from inspect import getargspec, isroutine
except Exception:
from inspect import getfullargspec as getargspec
`