title: How to filter multiple select values?
body: <p>I'm using selectpicker with fullcalendar, I've created a filter which works well with single values, but I can't make it works with selectpicker...</p>
  
  <p>Here is my <a href="https://plnkr.co/edit/odfOSlVZMJppLK68nIsU?p=preview" rel="nofollow noreferrer">plunker</a></p>
  
  <pre><code>eventRender: function(event, element) {
   var zone_class = event.className.toString();
  
  return ['all', zone_class].indexOf($('#zones_filter').val()) &gt;= 0;
  
  },
  </code></pre>
  
  <p>How can I add multiple values in the return?
  Thanks.</p>