Update docs/providers.rst code example

Co-authored-by: Mikhail Korobov <[email protected]>

Author: BurnzZ

docs/providers.rst

@@ -83,7 +83,7 @@ would lead to the following code:
         def __call__(self, to_provide: Set[Callable], response: Response):
             """Build a ``web_poet.HttpResponse`` instance using a Scrapy ``Response``"""
             return [
-                HttpResponse(
+                web_poet.HttpResponse(
                     url=response.url,
                     body=response.body,
                     status=response.status,