title: Set first day of week in momentjs - isoWeek
body: <p>Is it possible to set the first day of the week on Saturday for type isoweek?</p>
  
  <p>I want to get isoWeek number for first day of week is Saturday. But default in moment first day in isoWeek is Monday.</p>
  
  <p>I try something:</p>
  
  <pre><code>moment.lang('en', {week: {dow: 6, doy: 4}});
  </code></pre>
  
  <p>but its work fine only for <code>week()</code> (Saturday is first day of week):</p>
  
  <pre><code>moment(date).week()
  </code></pre>
  
  <p>for method <code>isoWeek()</code> its not working, becouse Monday is still first day of week.</p>
  
  <p>maybe somebody know a different way of getting the week number, where the first day of the week is Saturday and is used standard ISO 8601.</p>