bug in unity 5?

i follow this tutorial for making flapping bird,, but my bird "no go up" when i touch the screen https://www.youtube.com/watch?v=dWtoB3J1YTg

this is my script

 using UnityEngine;
 using System.Collections;
 
 public class SpermMovement : MonoBehaviour
 {
     Vector3 velocity = Vector3.zero;
     public Vector3 gravity;
     public Vector3 flapvelocity;
 
     bool didFlap = false;
     // Use this for initialization
     void Start(){
 
     }
     //DO GRAPHIC & INPUT UPDATE HERE
     void update() {
         if (Input.GetKeyDown(KeyCode.Space) || Input.GetMouseButtonDown(0) ) {
             didFlap = true;
         }
 
     }
 
     // DO PHYSICS ENGINE UPDATE HERE
     void FixedUpdate() { 
         velocity += gravity * Time.deltaTime;
         if (didFlap == true) { 
             didFlap = false;
             velocity += flapvelocity;
         }
         transform.position += velocity * Time.deltaTime;
 
 
     }
 }
 

please help