Fixed listening with --channels argument

[valericus]

I tried to run ./manage.py listen --channles my.fancy.Channel and faced with a couple of issues.

At first, there was a TypeError caused by missed order of arguments.

TypeError: isinstance() arg 2 must be a type, a tuple of types, or a union

When I've changed that order, another issue has risen, caused by missing argument for spawn mode.

manage.py listen: error: unrecognized arguments: my.fancy.Channel

So here is a fix for both issues.

[PaulGilmartin]

@valericus Thank you for your contribution to this library!