void Start()
    {
        EnemyFactoryScript factory = GameObject.FindGameObjectWithTag("Respawn")
                                     .GetComponent <EnemyFactoryScript>();

        StartCoroutine(GenerateWaves(factory));
        StartCoroutine(TimedScore());
    }
    private IEnumerator GenerateWaves(EnemyFactoryScript factory)
    {
        while (!GameOver)
        {
            yield return(new WaitForSeconds(WavesTimeout));

            Wave += 1;
            for (int i = 0; i < EnemiesCount; ++i)
            {
                factory.GenerateEnemy();
                yield return(new WaitForSeconds(EnemiesTimeout));
            }
        }
    }