Changed APIView.headers to Dict[str, str] (#114)

Author: MarcinWieczorek

rest_framework-stubs/views.pyi

@@ -30,7 +30,7 @@ class APIView(View):
     authentication_classes: Sequence[Type[BaseAuthentication]] = ...
     content_negotiation_class: Optional[str] = ...
     format_kwarg: Any = ...
-    headers: Any = ...
+    headers: Dict[str, str] = ...
     kwargs: Any = ...
     metadata_class: Optional[str] = ...
     parser_classes: Sequence[Type[BaseParser]] = ...