Notifications - fix pager

Summary: D10281 upgraded us to modern infrastructure but I think forget to set this little helper to return true. Fixes T5975.

Test Plan: paged through notifications with glee

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5975

Differential Revision: https://secure.phabricator.com/D10369

src/applications/notification/query/PhabricatorNotificationSearchEngine.php

@@ -136,4 +136,8 @@ final class PhabricatorNotificationSearchEngine
       ->appendChild($view);
   }
 
+  public function shouldUseOffsetPaging() {
+    return true;
+  }
+
 }