Fix a fatal in "create subtask"

Summary: This got clipped by the actor/email thing I think.

Test Plan: "Create Subtask" no longer fatals.

Reviewers: btrahan, vrana, hsb

Reviewed By: hsb

CC: aran, lesliepc16

Maniphest Tasks: T1918

Differential Revision: https://secure.phabricator.com/D3718

src/applications/maniphest/controller/ManiphestTaskEditController.php

@@ -250,7 +250,7 @@ final class ManiphestTaskEditController extends ManiphestController {
 
         if ($parent_task) {
           id(new PhabricatorEdgeEditor())
-            ->setUser($user)
+            ->setActor($user)
             ->addEdge(
               $parent_task->getPHID(),
               PhabricatorEdgeConfig::TYPE_TASK_DEPENDS_ON_TASK,