run black over stubs, add checking to travis

django-stubs-generated/core/exceptions.pyi

@@ -3,7 +3,6 @@ from typing import Any, Dict, Iterator, List, Optional, Tuple, Type, Union
 from django.db.models.base import Model
 from django.forms.utils import ErrorDict, ErrorList
 
-
 class FieldDoesNotExist(Exception): ...
 class AppRegistryNotReady(Exception): ...
 
@@ -43,12 +42,7 @@ class ValidationError(Exception):
             str,
         ],
         code: Optional[str] = ...,
-        params: Optional[
-            Union[
-                Dict[str, Union[Tuple[str], Type[Model], Model, str]],
-                Dict[str, Union[int, str]],
-            ]
-        ] = ...,
+        params: Optional[Union[Dict[str, Union[Tuple[str], Type[Model], Model, str]], Dict[str, Union[int, str]]]] = ...,
     ) -> None: ...
     @property
     def message_dict(self) -> Dict[str, List[str]]: ...