feat(BworserCapabilities): fix device change detection

Safari 11 has `navigator.mediaDevices.ondevicechange` but doesn't define
`navigator.mediaDevices.addEventListener`. 🤦

Fixes: https://github.com/jitsi/lib-jitsi-meet/issues/823

modules/browser/BrowserCapabilities.js

      */
     supportsDeviceChangeEvent() {
         return navigator.mediaDevices
-            && typeof navigator.mediaDevices.ondevicechange !== 'undefined';
+            && typeof navigator.mediaDevices.ondevicechange !== 'undefined'
+            && typeof navigator.mediaDevices.addEventListener !== 'undefined';
     }
 
     /**