emit `error` event instead of throw error

I think just emit `error` event is better than throw it on `ConnectionManager.prototype.onSocketData()`.

When network come wrong, the zk response data will fault. And `node-zookeeper-client` throw error when data format incorrect, it will let node process exit.

I think use `error` event is better. If use care about `error`, he will listen the `error` event and reconnect zk server again.

@see alibaba/node-hbase-client#22