How to add "Press ESC to EXIT"? and exit the game?

I'm having trouble.

This is the "Done_GameController" script in which i've added if (Input.GetKeyDown(KeyCode.Escape)) { Application.Quit(); }

Pressing ESC do nothing, I don't undersatand why?

using UnityEngine; using System.Collections;

public class Done_GameController : MonoBehaviour { public GameObject[] hazards; public Vector3 spawnValues; public int hazardCount; public float spawnWait; public float startWait; public float waveWait;

 public GUIText scoreText;
 public GUIText restartText;
 public GUIText gameOverText;
 
 private bool gameOver;
 private bool restart;
 private int score;
 
 void Start ()
 {
     gameOver = false;
     restart = false;
     restartText.text = "";
     gameOverText.text = "";
     score = 0;
     UpdateScore ();
     StartCoroutine (SpawnWaves ());
 }
 
 void Update ()
 {
     if (restart)
     {
         if (Input.GetKeyDown (KeyCode.R)) {
             Application.LoadLevel (Application.loadedLevel);
         }
         if (Input.GetKeyDown(KeyCode.Escape))
             {
                 Application.Quit();
             }


     }
 }
 
 IEnumerator SpawnWaves ()
 {
     yield return new WaitForSeconds (startWait);
     while (true)
     {
         for (int i = 0; i < hazardCount; i++)
         {
             GameObject hazard = hazards [Random.Range (0, hazards.Length)];
             Vector3 spawnPosition = new Vector3 (Random.Range (-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
             Quaternion spawnRotation = Quaternion.identity;
             Instantiate (hazard, spawnPosition, spawnRotation);
             yield return new WaitForSeconds (spawnWait);
         }
         yield return new WaitForSeconds (waveWait);
         
         if (gameOver)
         {
             restartText.text = "Press 'R' for Restart";
             restart = true;
             break;
         }
     }
 }
 
 public void AddScore (int newScoreValue)
 {
     score += newScoreValue;
     UpdateScore ();
 }
 
 void UpdateScore ()
 {
     scoreText.text = "Score: " + score;
 }
 
 public void GameOver ()
 {
     gameOverText.text = "Game Over!";
     gameOver = true;
 }

}