Fix issue #1055 (#1056)

* Fix issue #1055

* Fix if to elif

* Use self.stdout.write instead of print when printing graphql schema

Co-authored-by: leonardo arroyo <[contato@leonardoarroyo.com](mailto:contato@leonardoarroyo.com)>

graphene_django/management/commands/graphql_schema.py

@@ -60,8 +60,10 @@ def save_graphql_file(self, out, schema):
 
     def get_schema(self, schema, out, indent):
         schema_dict = {"data": schema.introspect()}
-        if out == "-":
+        if out == "-" or out == "-.json":
             self.stdout.write(json.dumps(schema_dict, indent=indent, sort_keys=True))
+        elif out == "-.graphql":
+            self.stdout.write(print_schema(schema))
         else:
             # Determine format
             _, file_extension = os.path.splitext(out)