Update fullcalendar (#730)

Author: jarrodmillman

layouts/calendars/list.html

@@ -32,8 +32,8 @@ <h5 class="subtitle">{{ .Params.Subtitle }}</h5>
         <br>
         <script src="https://cdn.jsdelivr.net/npm/vega@5"></script>
         <script src="https://cdnjs.cloudflare.com/ajax/libs/ical.js/1.5.0/ical.min.js"></script>
-        <script src='https://cdn.jsdelivr.net/npm/fullcalendar@6.1.11/index.global.min.js'></script>
-        <script src="https://cdn.jsdelivr.net/npm/@fullcalendar/icalendar@6.1.11/index.global.min.js"></script>
+        <script src='https://cdn.jsdelivr.net/npm/fullcalendar@6.1.15/index.global.min.js'></script>
+        <script src="https://cdn.jsdelivr.net/npm/@fullcalendar/icalendar@6.1.15/index.global.min.js"></script>
         <script>
           document.addEventListener('DOMContentLoaded', function() {
             var cal_colors = vega.scheme('category10');