title: SimpleDateFormat ignores "XXX" if timezone is set to "UTC"
body: <p>I am trying to output the current datetime as UTC in the following format:
  2016-01-11T14:08:42+00:00</p>
  
  <pre><code>final SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssXXX");
  formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
  
  final String dateString = formatter.format(new Date());
  </code></pre>
  
  <p>"dateString" should now contain "2016-01-11T14:08:42+00:00" but it contains "2016-01-11T14:08:42Z".</p>
  
  <p>Without the "UTC" timezone setting I get the right format but - of course - in my specific timezone...</p>
  
  <p>Any ideas?</p>