function Worker( queue, type ) {
  this.queue   = queue;
  this.type    = type;
  this.client  = Worker.client || (Worker.client = redis.createClient());
  this.running = true;
  this.job     = null;
}
Initialize a new `Worker` with the given Queue
targetting jobs of `type`.

@param {Queue} queue
@param {String} type
@api private