bug in Worker.scala, ExecutorRunner is not serializable

[Huangguowei]

In Worker.scala line 480:

    case RequestWorkerState =>
      sender ! WorkerStateResponse(host, port, workerId, 
executors.values.toList,
        finishedExecutors.values.toList, drivers.values.toList,
        finishedDrivers.values.toList, activeMasterUrl, cores, memory,
        coresUsed, memoryUsed, activeMasterWebUiUrl)

The executors's type is:
val executors = new HashMap[String, ExecutorRunner]

but ExecutorRunner cannot be Serialized, so if ask RequestWorkerState will 
cause java.io.NotSerializableException.