Double Jump Not Working

Hello, I was following the LMG tutorial on Infinite Runner 2d. I could not jump as I was supposed to in the video perhaps because I am using unity 5 and the video was unity 4. I am a beginner. I cannot double jump but I can jump once.

Code:

 using System;
 using UnityEngine;
 
 namespace UnityStandardAssets._2D
 {
     public class PlatformerCharacter2D : MonoBehaviour
     {
         [SerializeField] private float m_MaxSpeed = 10f;                    // The fastest the player can travel in the x axis.
         [SerializeField] private float m_JumpForce = 400f;                  // Amount of force added when the player jumps.
         [Range(0, 1)] [SerializeField] private float m_CrouchSpeed = .36f;  // Amount of maxSpeed applied to crouching movement. 1 = 100%
         [SerializeField] private bool m_AirControl = false;                 // Whether or not a player can steer while jumping;
         [SerializeField] private LayerMask m_WhatIsGround;                  // A mask determining what is ground to the character
 
         private Transform m_GroundCheck;    // A position marking where to check if the player is grounded.
         const float k_GroundedRadius = .2f; // Radius of the overlap circle to determine if grounded
         private bool m_Grounded;            // Whether or not the player is grounded.
         private Transform m_CeilingCheck;   // A position marking where to check for ceilings
         const float k_CeilingRadius = .01f; // Radius of the overlap circle to determine if the player can stand up
         private Animator m_Anim;            // Reference to the player's animator component.
         private Rigidbody2D m_Rigidbody2D;
         private bool m_FacingRight = true;  // For determining which way the player is currently facing.
 
         **bool doubleJump = false;**
 
         private void Awake()
         {
             // Setting up references.
             m_GroundCheck = transform.Find("GroundCheck");
             m_CeilingCheck = transform.Find("CeilingCheck");
             m_Anim = GetComponent<Animator>();
             m_Rigidbody2D = GetComponent<Rigidbody2D>();
         }
 
 
         private void FixedUpdate()
         {
             m_Grounded = false;
 
             // The player is grounded if a circlecast to the groundcheck position hits anything designated as ground
             // This can be done using layers instead but Sample Assets will not overwrite your project settings.
             Collider2D[] colliders = Physics2D.OverlapCircleAll(m_GroundCheck.position, k_GroundedRadius, m_WhatIsGround);
             for (int i = 0; i < colliders.Length; i++)
             {
                 if (colliders[i].gameObject != gameObject)
                     m_Grounded = true;
             }
             m_Anim.SetBool("Ground", m_Grounded);
 
             // Set the vertical animation
             m_Anim.SetFloat("vSpeed", m_Rigidbody2D.velocity.y);
 
             **if (m_Grounded)
                 doubleJump = false;**
         }
 
 
         public void Move(float move, bool crouch, bool jump)
         {
             // If crouching, check to see if the character can stand up
             if (!crouch && m_Anim.GetBool("Crouch"))
             {
                 // If the character has a ceiling preventing them from standing up, keep them crouching
                 if (Physics2D.OverlapCircle(m_CeilingCheck.position, k_CeilingRadius, m_WhatIsGround))
                 {
                     crouch = true;
                 }
             }
 
             // Set whether or not the character is crouching in the animator
             m_Anim.SetBool("Crouch", crouch);
 
             //only control the player if grounded or airControl is turned on
             if (m_Grounded || m_AirControl)
             {
                 // Reduce the speed if crouching by the crouchSpeed multiplier
                 move = (crouch ? move*m_CrouchSpeed : move);
 
                 // The Speed animator parameter is set to the absolute value of the horizontal input.
                 m_Anim.SetFloat("Speed", Mathf.Abs(move));
 
                 // Move the character
                 m_Rigidbody2D.velocity = new Vector2(move*m_MaxSpeed, m_Rigidbody2D.velocity.y);
 
                 // If the input is moving the player right and the player is facing left...
                 if (move > 0 && !m_FacingRight)
                 {
                     // ... flip the player.
                     Flip();
                 }
                     // Otherwise if the input is moving the player left and the player is facing right...
                 else if (move < 0 && m_FacingRight)
                 {
                     // ... flip the player.
                     Flip();
                 }
             }
             **// If the player should jump...
             if ((m_Grounded || !doubleJump) && jump && m_Anim.GetBool("Ground"))
                 {
                 // Add a vertical force to the player.
                 m_Grounded = false;
                 m_Anim.SetBool("Ground", false);
                 m_Rigidbody2D.velocity = new Vector2(m_Rigidbody2D.velocity.x , 0);
                 
                 
                 m_Rigidbody2D.AddForce(new Vector2(0f, m_JumpForce));
                 if(!m_Grounded){
                     doubleJump = true;
                 }
             }
             
             
         }**
 
 
         private void Flip()
         {
             // Switch the way the player is labelled as facing.
             m_FacingRight = !m_FacingRight;
 
             // Multiply the player's x local scale by -1.
             Vector3 theScale = transform.localScale;
             theScale.x *= -1;
             transform.localScale = theScale;
         }
     }
 }