Using iTween's Turret Example on 2D environment

I am trying to use iTween's Turret Example. I did everything good so far except following mouse position with rotating turret.

I have a turret as you can see in the image above and I want it to follow the target(Mouse Position) by rotating around it self. For that, iTween has great example but it is only for 3d :( So, I tried to implement it in 2D but whatever I did I couldn't succeed.

 using UnityEngine;
 using System.Collections;
 
 public class CannonController : MonoBehaviour
 {
         public Rigidbody2D bullet;
         public Camera mainCam;
         public GameObject pivot;
         float pivotX;
         float pivotY;
 
 
         public Transform target;
         float smoothTime = 0.3f;
         float xOffset = 1f;
         float yOffset = 1f;
         Vector2 velocity;
         Transform thisTransform;
          
 
 
         void Start ()
         {
                 thisTransform = transform;
         }
         // Update is called once per frame
         void Update ()
         {
                 pivotX = pivot.transform.position.x;
                 pivotY = pivot.transform.position.y;
 
 
                 //rotation:
                 Vector2 mousePos = Camera.main.ScreenToWorldPoint (Input.mousePosition);
                 mousePos.y = 0;
                 gameObject.transform.rotation = Quaternion.Euler (new Vector3 (mousePos.x, 0, mousePos.y));
                 Vector2 worldPos = Camera.main.ScreenToWorldPoint (mousePos);
                 iTween.LookUpdate (gameObject, iTween.Hash ("looktarget", worldPos, "time", 2, "axis", "y"));
 
 
                 //rotation:
 //                Vector3 mousePos = Camera.main.ScreenToWorldPoint (Input.mousePosition);
 //                mousePos.z = 0;
 //                gameObject.transform.position = mousePos;
 //                Vector3 worldPos = Camera.main.ScreenToWorldPoint (mousePos);
 //                iTween.LookUpdate (gameObject, iTween.Hash ("looktarget", worldPos, "time", 2, "axis", "y"));
         
                 //fire:
                 if (Input.GetMouseButtonDown (0)) {
                         Rigidbody2D clone = (Rigidbody2D)Instantiate (bullet, new Vector2 (pivotX, pivotY), transform.rotation);
                         clone.velocity = transform.TransformDirection (Vector2.up * 10f);
                 }
         }
 }
 

Commented parts under "rotation:" was the iTween's original code for rotating by following mouse position for 3D environment. The other parts under "rotation:" with Vector2 code is my code.

This was the closest trial I could ever made, but I it is not really working. It only moves the turret on x-axis just a little bit (not much!) But I guess, the turret should be rotate around z-axis. So, can anyone help me to rotate the turret around z-axis smoothly by following mouse position ?