title: FullCalendar adds "undefined" next to each date
body: <p>I am using <a href="https://github.com/CroudSupport/vue-fullcalendar" rel="nofollow noreferrer">vue-fullcalendar</a> which is a wrapper for <a href="https://fullcalendar.io/" rel="nofollow noreferrer">FullCalendar</a> library. I've set up the calendar and it is working fine, but as soon I import <a href="https://fullcalendar.io/docs/scheduler/" rel="nofollow noreferrer">Scheduler</a>, which is add-on that provides FullCalendar functionality to display resources I got "undefined" next to each date in the calendar (As you can see on the image).</p>
  
  <p><a href="https://i.stack.imgur.com/WqgSx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WqgSx.png" alt="enter image description here"></a></p>
  
  <p>I found two articles on the stackoverflow about this issue:</p>
  
  <ol>
  <li><a href="https://stackoverflow.com/questions/43227050/jquery-fullcalendar-displayed-undefined-on-title">jQuery fullCalendar displayed undefined on title</a> - I have tried to change the order of moment.js but that doesn't help. This issue is also happening even if I not impor moment.js at all.</li>
  <li><a href="https://stackoverflow.com/questions/43691292/how-to-edit-title-in-fullcalendar">How to edit Title in Fullcalendar</a> - Also tried to revert to older version of FullCalendar but without success.</li>
  </ol>
  
  <p>This is the code that I am using:</p>
  
  <pre><code>&lt;template&gt;
  &lt;div&gt;
      &lt;full-calendar
              ref="calendar"
              :events="events"
              :config="config"
      &gt;
      &lt;/full-calendar&gt;
  &lt;/div&gt;
  &lt;/template&gt;
  
  &lt;script&gt;
    import * as moment from 'moment'
    import {FullCalendar} from 'vue-full-calendar'
    import 'fullcalendar/dist/fullcalendar.min.css'
    import 'fullcalendar-scheduler'
    import "fullcalendar-scheduler/dist/scheduler.min.css"
  
    export default {
      data() {
        return {
          config: {},
  
          events: [
            {
              id: 1,
              title: 'Title',
              start: moment().add(2, 'd').add(2, 'h'),
              end: moment().add(2, 'd').add(4, 'h'),
              resourceId: 'a'
            }
          ]
        }
      },
  
      methods: {},
  
      components: {
        FullCalendar
      }
  
    }
  &lt;/script&gt;
  </code></pre>