Unity face camera, keep up direction

FaceCamera.cs

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class FaceCamera : MonoBehaviour
{


	public bool faceCameraActive = true;
	public Camera targetCamera;
	public float rotateSpeed = 1.0f;

	// Use this for initialization
	void Start ()
	{
		if (targetCamera == null) {
			targetCamera = Camera.main;
		}
	}

	void Update ()
	{
		if (!faceCameraActive) {
			return;
		}
		Vector3 localCamPosition = transform.InverseTransformPoint (targetCamera.transform.position);
		localCamPosition = new Vector3 (localCamPosition.x, 0, localCamPosition.z);
		Vector3 lookTarget = transform.TransformPoint (localCamPosition);
		Vector3 targetDirection = (lookTarget - transform.position).normalized;
		//transform.LookAt (lookTarget, transform.up);
		Quaternion tr = Quaternion.LookRotation (lookTarget, transform.up);
		transform.rotation = Quaternion.Slerp (transform.rotation, tr, Time.deltaTime * rotateSpeed);
	}

	public void OnDrawGizmos ()
	{
		Vector3 localCamPosition = transform.InverseTransformPoint (targetCamera.transform.position);
		localCamPosition = new Vector3 (localCamPosition.x, 0, localCamPosition.z);
		Vector3 lookTarget = transform.TransformPoint (localCamPosition);
		Vector3 targetDirection = (lookTarget - transform.position).normalized;
		Gizmos.color = Color.red;
		Gizmos.DrawSphere (transform.position + targetDirection, 0.01f);
		Gizmos.DrawCube (lookTarget, Vector3.one * 0.03f);
	}
}