title: Fullcalendar columnheaderformat attribute
body: <p>I'm using fullcalendar (v3) and I can't configure properly the <em>columnheaderformat</em> attribute. Thanks in advance.</p>
  
  <pre><code>$('#calendar').fullCalendar({
       locale: 'es',
       firstDay: 1,
       defaultView: 'agendaWeek',
       header: false,
       footer: false,
       allDaySlot : false,
       slotEventOverlap: false,
       columnHeaderFormat: 'ddd'
  });
  </code></pre>