Use the correct "completed" time in Harbormaster display UI

Summary: Fixes T12883. The task seems correct to me and I think this is a copy/paste mistake that probably blames to me.

Test Plan: Fiddled these numbers, viewed a build in Harbormaster, saw the adjusted time.

Reviewers: chad, amckinley

Reviewed By: chad

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T12883

Differential Revision: https://secure.phabricator.com/D18177

Author: epriestley

src/applications/harbormaster/controller/HarbormasterBuildViewController.php

@@ -141,7 +141,7 @@ public function handleRequest(AphrontRequest $request) {
         if ($ended) {
           $when[] = pht(
             'Completed at %s',
-            phabricator_datetime($started, $viewer));
+            phabricator_datetime($ended, $viewer));
 
           $duration = ($ended - $started);
           if ($duration) {