Update to graphene 3

[ldynia]

Hi @prokher

I am wondering if you are gonna create a pre-release of the project to support graphene 3, and when would that be ?

Best

[W-Varg]

x2
django-graphql-jwt use graphene 3 but this package not yet, so the error skips

django-channels-graphql-ws 0.8.0 requires graphene<3.0,>=2.1, but you have graphene 3.0b7 which is incompatible.

[prokher]

Closing this as a duplicate of #45.