Fix missing colon in function definition (#1030)

docs/testing.rst

@@ -94,7 +94,7 @@ To use pytest define a simple fixture using the query helper below
         from graphene_django.utils.testing import graphql_query
 
         @pytest.fixture
-        def client_query(client)
+        def client_query(client):
             def func(*args, **kwargs):
                 return graphql_query(*args, **kwargs, client=client)
 
@@ -115,4 +115,4 @@ To use pytest define a simple fixture using the query helper below
             )
 
             content = json.loads(response.content)
-            assert 'errors' not in content
+            assert 'errors' not in content