join method
Join a room (first/created on the server). Re-joined automatically on
reconnect. Returns the server's acknowledgement ({ ok, room, related }).
Implementation
Future<dynamic> join(String room) {
_rooms.add(room);
NexusLog.info('realtime join "$room"');
return _ackEmit('room.join', {'name': room}, label: 'join "$room"');
}