title: Error '.xls' is in a different format than specified by the file extension
body: <p>I found a plugin that helps me export ExtJS grid data into MS Excel sheet.
  <a href="http://druckit.wordpress.com/2013/10/26/generate-an-excel-file-from-an-ext-js-4-grid/" rel="nofollow noreferrer">http://druckit.wordpress.com/2013/10/26/generate-an-excel-file-from-an-ext-js-4-grid/</a></p>
  
  <p>all works great except for the error I'm getting before opening the file.</p>
  
  <p><img src="https://i.stack.imgur.com/TvNtT.png" alt="enter image description here"></p>
  
  <p>Peace of my code:</p>
  
  <pre><code>if (Ext.isChrome || Ext.isGecko) { // local download
              var gridEl = this.getEl();
  
              var el = Ext.DomHelper.append(gridEl, {
                  tag: "a",
                 download: title + "-" + Ext.Date.format(new Date(), 'Y-m-d') + '.xls',
                 href: location
              });
  
              el.click();
  
              Ext.fly(el).destroy();
  
          }
  </code></pre>
  
  <p>One solution suggested that i remove the apostrophe so i tried:</p>
  
  <pre><code>download: title + "-" + Ext.Date.format(new Date(), "Y-m-d") + ".xls",
  </code></pre>
  
  <p>But no luck. Any idea?</p>