title: Sencha cmd 5 minify issue
body: <p>I am trying to minify sencha 5 project with sencha cmd, but it always failed.</p>
  
  <blockquote>
    <p>sencha generate app -ext demoApp ./demoApp</p>
  </blockquote>
  
  <p>Then I try to minify the app, by typing </p>
  
  <blockquote>
    <p>sencha app build production</p>
  </blockquote>
  
  <p>For blank project, the minify success, I can run in my local web server.  Then I change the existing project that have been created, just add one button to display popup window (and the information displayed by xtype "displayfield").</p>
  
  <p>Before it minified &amp; after add one button to display popup, it works normal (tested in browser, click the button, the popup and information showed correctly).  After minified, it doesn't work, </p>
  
  <p><em>GET <a href="http://localhost/test/sencha/demoApp/widget/displayfield.js?_dc=1429726459576" rel="nofollow">http://localhost/test/sencha/demoApp/widget/displayfield.js?_dc=1429726459576</a> 404 not found.</em> </p>
  
  <p><em>"NetworkError: 404 Not Found - <a href="http://localhost/test/sencha/demoApp/widget/displayfield.js?_dc=1429726459576" rel="nofollow">http://localhost/test/sencha/demoApp/widget/displayfield.js?_dc=1429726459576</a>"</em></p>
  
  <p>Is it weird?  If I change the xtype "displayfield" to "textfield" it works normal, or if I change to "button" and change fieldLabel to text, it works!</p>
  
  <p>Anyone have succesfull minify sencha 5 with sencha cmd?  My Sencha Cmd version is 5.1.2.52 and I use sencha 5.1.0.107.</p>
  
  <p>I attach the original app folder code original in <a href="http://www.didud.com/app_original.zip" rel="nofollow">here</a> and my changes app code in <a href="http://www.didud.com/app.zip" rel="nofollow">here</a></p>
  
  <p>Many thanks!</p>