fix fatal - setViewer => setUser

Summary: D4249 missed a spot I think.

Test Plan: no more fatal

Reviewers: vrana, epriestley

Reviewed By: vrana

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4270

src/applications/feed/builder/PhabricatorFeedBuilder.php

@@ -54,7 +54,7 @@ final class PhabricatorFeedBuilder {
       }
 
       $view = $story->renderView();
-      $view->setViewer($user);
+      $view->setUser($user);
 
       $null_view->appendChild($view);
     }