Fix type of PageNumberPagination.page (#51)

PR #46 set as the incorrect type. Its actual type is Page.

See: https://github.com/encode/django-rest-framework/blob/de497a9bf12605b8b71bf7c21da57bc2a8238786/rest_framework/pagination.py#L206

Author: brianhelba

rest_framework-stubs/pagination.pyi

@@ -1,6 +1,6 @@
 from typing import Any, Callable, Dict, List, NamedTuple, Optional, Sequence, Tuple, Type, Union
 
-from django.core.paginator import Paginator, SupportsCount, SupportsLen
+from django.core.paginator import Page, Paginator, SupportsCount, SupportsLen
 from django.db.models import QuerySet
 from django.http import HttpRequest
 from django.views import View
@@ -54,7 +54,7 @@ class PageNumberPagination(BasePagination):
     invalid_page_message: str = ...
 
     # Instance attributes dynamically added by paginate_queryset
-    page: Optional[Paginator] = ...
+    page: Optional[Page] = ...
     request: Optional[HttpRequest] = ...
     def get_page_size(self, request: Request) -> int: ...
     def get_next_link(self) -> Optional[str]: ...