Add support for Graphene3 and update lint with black (#72)

dev-env-requirements.txt

graphene_django_optimizer/field.py

graphene_django_optimizer/query.py

tests/graphql_utils.py

tests/schema.py

tests/test_field.py

tests/test_query.py

tests/test_relay.py

tests/test_resolver.py

tests/test_types.py