Raycast LineRenderer, how to set end direction of Ray by transform to the center of the screen or crosshair?

I try to do a simple fps, and I just can't figure how I can do this. I need to change lane 82 of my script to be center of my screen or crosshair, any guidance?

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class PlayerShooting : MonoBehaviour
 {
     public int minDmg = 15;
     public int maxDmg = 25;
     public float timeBetweenBullets = 0.15f;
     public float range = 50;
     
     public Texture crossHair;
     public Rect middle;
 
     Ray shootRay;
     RaycastHit shootHit;
     ParticleSystem gunParticles;
     LineRenderer gunLine;
     AudioSource gunAudio;
     Light gunLight;
     int shootableMask;
     float effectsDisplayTime = 0.2f;
     float timer;
 
 
     void OnGUI() 
     {
         GUI.DrawTexture (middle, crossHair);
     }
     
     
     void Awake ()
     {
         shootableMask = LayerMask.GetMask ("Shootable");
         gunParticles = GetComponent<ParticleSystem> ();
         gunLine = GetComponent <LineRenderer> ();
         gunAudio = GetComponent<AudioSource> ();
         gunLight = GetComponent<Light> ();
     }
 
 
     void Update ()
     {
         timer += Time.deltaTime;
 
         middle = new Rect((Screen.width - crossHair.width/4) / 2, (Screen.height - crossHair.height/4) /2, crossHair.width /4, crossHair.height/4);
         
         if(Input.GetButton ("Fire1") && timer >= timeBetweenBullets && Time.timeScale != 0)
         {
             Shoot ();
         }
 
         if(timer >= timeBetweenBullets * effectsDisplayTime)
         {
             DisableEffects ();
         }
     }
 
 
     public void DisableEffects ()
     {
         gunLine.enabled = false;
         gunLight.enabled = false;
     }
 
 
     void Shoot ()
     {
         timer = 0f;
 
         gunAudio.Play ();
          
         gunLight.enabled = true;
 
         gunParticles.Stop ();
         gunParticles.Play ();
 
         gunLine.enabled = true;
         gunLine.SetPosition (0, transform.position);
 
         shootRay.origin = transform.position;
         shootRay.direction = transform.forward;     //I NEED THIS TO BE THE CENTER OF MY SCREEN OR CENTER OF MY CROSSHAIR
 
         if(Physics.Raycast (shootRay, out shootHit, range, shootableMask))
         {
             EnemyHealth enemyHealth = shootHit.collider.GetComponent <EnemyHealth> ();
             if(enemyHealth != null)
             {
                 enemyHealth.TakeDamage (Random.Range(minDmg, maxDmg), shootHit.point);
             }
             gunLine.SetPosition (1, shootHit.point);
         }
         else
         {
             gunLine.SetPosition (1, shootRay.origin + shootRay.direction * range);
         }
     }
 }