message: Use m.custom for widget type
  As per
diff: @@ -620,7 +620,7 @@ export const CommandMap = {
  const nowMs = (new Date()).getTime();
  const widgetId = encodeURIComponent(`${roomId}_${userId}_${nowMs}`);
  return success(WidgetUtils.setRoomWidget(
  - roomId, widgetId, "customwidget", args, "Custom Widget", {}));
  + roomId, widgetId, "m.custom", args, "Custom Widget", {}));
  } else {
  return reject(_t("You cannot modify widgets in this room."));
  }
  