title: Get Last Month Date In Flutter / Dart
body: <p>in flutter we can get current month using this </p>
  
  <pre><code>var now = new DateTime.now();
  var formatter = new DateFormat('MM');
  String month = formatter.format(now);
  </code></pre>
  
  <p>But how to get the last month date? Especially if current date is January (01). we can't get the right month when we use operand minus (-) , like month - 1. </p>