fixed RedisClient.prototype.end not clear this.retry_timer

we call redisClient.end(),but the redisClient.end function does not clear this.retry_timer.
this.retry_timer is waiting for timeout to reconnect redis.
when redis is closed,this.stream will throw "error" event,redisClient does not catch it.and the process will exit.

see https://github.com/mranney/node_redis/issues/476#issuecomment-44226272
thanks.