Link directly to the http options in upgrade guide

Author: tilgovi

doc/upgrading.rst

@@ -142,7 +142,7 @@ Auth plugin
 
 The auth plugin, which in 1.2 retrieved an authentication token from an API
 endpoint and set up the Store plugin, is not available for 2.0. See the
-documentation for the :func:`annotator.storage.http` module for configuring
+documentation for :data:`annotator.storage.HttpStorage.options` for configuring
 the request headers directly according to your needs.