private void Update()
{
speed += speedIncrease *Time.deltaTime;
}
public void SpawnWave()
{
int rand = Random.Range(0, wall.Lenght);
Vector3 random_value = new Vector3(Random.Range(0, 0,1f),0,0);
Instantiate(wall[rand], transform.position+random_value, Quaternion.identity);
}