Fix test for "last updated" text.

Tools/GardeningServer/ui/ct-last-updated.html

 <!--
 Copyright 2014 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <polymer-element name="ct-last-updated" attributes="date">
   <template>
     <template if="{{ date }}">
       Updated {{ date | _deltaMinutes }} min ago @ {{ date | _hours }}:{{ date | _minutes }}
     </template>
   </template>
   <script>
   (function() {
     Polymer({
       date: null,
 
       _deltaMinutes: function(date) {
         return date.minutesAgo();
       },
       _hours: function(date) {
         return date.getHours();
       },
       _minutes: function(date) {
-        var s = date.getMinutes().toString();
-        if (s.length == 1)
-          s = "0" + s;
-        return s;
+        return date.getMinutes().toString().padLeft(2, '0');
       },
     });
   })();
 
   </script>
 </polymer-element>