title: Pikaday date range don't work
body: <p>I used the range function from pikaday.</p>
  
  <p>with onSelectI set the date range what actually works.
  Here is my example:</p>
  
  <pre><code>onSelect: function(date) {
      var first_ = (date.getDate() - date.getDay())+1;
      var last_ = first_ + 4;
  
      var firstday = new Date(date.setDate(first_));
      var lastday = new Date(date.setDate(last_));
  
      picker.setStartRange(firstday);
      picker.setEndRange(lastday);
  
      picker.draw();
  
      var f_startdate = firstday.getDate()+'.'+(firstday.getMonth()+1)+'.'+firstday.getFullYear();
      var f_enddate = lastday.getDate()+'.'+(lastday.getMonth()+1)+'.'+lastday.getFullYear();
      var kw = getWeekNumber(date.getFullYear()+'/'+(date.getMonth()+1)+'/'+date.getDate());
  
      document.getElementById('calendar').value = f_startdate+' - '+f_enddate;
      // document.getElementById('calendar').value = 'KW: '+(kw+1);
  }
  </code></pre>
  
  <p>But when I select the 03.06.2016 the range is set to the "30.05.2016 - 03.05.2016" and the Input is wrong. Maybe anyone can help me.</p>
  
  <p>Here is a working example: <a href="https://jsfiddle.net/24aL9f21/1/" rel="nofollow">https://jsfiddle.net/24aL9f21/1/</a></p>