run black over stubs, add checking to travis

django-stubs-generated/db/backends/mysql/client.pyi

@@ -2,17 +2,10 @@ from typing import Any, Dict, List, Optional, Union
 
 from django.db.backends.base.client import BaseDatabaseClient
 
-
 class DatabaseClient(BaseDatabaseClient):
     executable_name: str = ...
     @classmethod
     def settings_to_cmd_args(
-        cls,
-        settings_dict: Dict[
-            str,
-            Optional[
-                Union[Dict[str, Dict[str, str]], int, str]
-            ],
-        ],
+        cls, settings_dict: Dict[str, Optional[Union[Dict[str, Dict[str, str]], int, str]]]
     ) -> List[str]: ...
     def runshell(self) -> None: ...