run black over stubs, add checking to travis

django-stubs-generated/views/decorators/clickjacking.pyi

@@ -1,6 +1,5 @@
 from typing import Any, Callable, Optional
 
-
 def xframe_options_deny(view_func: Callable) -> Callable: ...
 def xframe_options_sameorigin(view_func: Callable) -> Callable: ...
 def xframe_options_exempt(view_func: Callable) -> Callable: ...