channels 3 requires redis 5 and code changes

channels>=3 (Oct 2020) requires redis>=5 in Linux and minor code changes for ASGI 3.

Clues include:

ERROR: TypeError: object.__init__() takes exactly one argument (the instance to initialize)

and:

aioredis.errors.ReplyError: ERR unknown command 'BZPOPMIN'

https://channels.readthedocs.io/en/latest/releases/3.0.0.html#release-notes