void InitiatePizzaResupply(DeliveryTruck receiver)
 {
     //make sure the truck is going slow enough to receive pizzas
     if (receiver.GetComponent <Rigidbody>().velocity.magnitude < speedTolerance)
     {
         //it is! wait a sec, then drop the 'zas
         supplying            = true;
         pizzasToGiveThisTrip = truck.getMaxPizzas() - truck.HowManyPizzas();
         spawnTimer           = delayBeforeResupply;
     }
 }
    // Update is called once per frame
    void OnTriggerStay(Collider other)
    {
        //if there's a truck in the bay, start resupplying pizzas!
        if (other.gameObject.CompareTag("DeliveryTruck"))
        {
            truck = other.GetComponent <DeliveryTruck>();

            //if the truck's already got enough pizzas, ignore it
            if (truck.HowManyPizzas() >= truck.getMaxPizzas())
            {
                return;
            }

            if (supplying == false)
            {
                InitiatePizzaResupply(truck);
            }
        }
    }