message: fix last remaining broken test
diff: @@ -436,8 +436,8 @@ describe('MessagePanel', function() {
  const rm = res.find('.mx_RoomView_myReadMarker_container').getDOMNode();
  const rows = res.find('.mx_RoomView_MessageList').children();
  - expect(rows.length).toEqual(6);
  - expect(rm.previousSibling).toEqual(rows.at(4).getDOMNode());
  + expect(rows.length).toEqual(7); // 6 events + the NewRoomIntro
  + expect(rm.previousSibling).toEqual(rows.at(5).getDOMNode());
  // read marker should be hidden given props and at the last event
  expect(isReadMarkerVisible(rm)).toBeFalsy();
  