fix demo

demos/background-events.html

@@ -43,13 +43,13 @@
 
         // areas where "Meeting" must be dropped
         {
-          id: 'availableForMeeting',
+          groupId: 'availableForMeeting',
           start: '2018-04-11T10:00:00',
           end: '2018-04-11T16:00:00',
           rendering: 'background'
         },
         {
-          id: 'availableForMeeting',
+          groupId: 'availableForMeeting',
           start: '2018-04-13T10:00:00',
           end: '2018-04-13T16:00:00',
           rendering: 'background'