title: How do I format DateTime with UTC timezone offset?
body: <p>What type of date format is this?</p>
  <pre><code>2020-03-26T00:57:08.000+08:00
  </code></pre>
  <p>I'm using <a href="https://api.flutter.dev/flutter/intl/DateFormat-class.html" rel="nofollow noreferrer">DateFormat</a> class</p>
  <pre><code> DateTime dateTime = DateTime.now();
  
   print(dateTime.toIso8601String());
   print(dateTime.toLocal());
   print(dateTime.toUtc());
  </code></pre>
  <p>Output</p>
  <pre><code>I/flutter (20667): 2020-03-26T01:34:20.826589
  I/flutter (20667): 2020-03-26 01:34:20.826589
  I/flutter (20667): 2020-03-25 17:34:20.826589Z
  </code></pre>
  <p>I would like to have a date format like the first output I show, which has the +08:00 behind. Which should I use?</p>