Enemy shake/vibrate when following character

I am using the arongranberg A* path finding project to create way points for one enemy to follow the player. However, the enemy vibrates back and forward by about 0.1 - 0.2 unit distance when moving. I have done a lot of research regarding this problem in the past few days but to no avail I could not find a solution that solves it. This is link to a gif to show what I mean.

I have tried,

changing Application.targetFrameRate = 30;

changing fixed update to update and vice versa;

using rigidbody2d and turn interpolate on plus using velocity to move;

turning iskinematic on and off;

using translate to move.

none of the above solution works. Below is the script I have for my enemy. Any advice would be appreciated.

    using UnityEngine;
    using System.Collections;
    //Note this line, if it is left out, the script won't know that the class 'Path' exists and it will throw compiler errors
    //This line should always be present at the top of scripts which use pathfinding
    using Pathfinding;

public class AstarAI : MonoBehaviour
	//The point to move to
	public Transform target;

	private Seeker seeker;

	//The calculated path
	public Path path;

	//The AI's speed per second
	public float speed = 200;

	//The max distance from the AI to a waypoint for it to continue to the next waypoint
	public float nextWaypointDistance = 0.02f;

	//The waypoint we are currently moving towards
	private int currentWaypoint = 0;

	Rigidbody2D rb;

	public void Start ()
		rb = this.GetComponent<Rigidbody2D> ();
		seeker = GetComponent<Seeker>();

		//Start a new path to the targetPosition, return the result to the OnPathComplete function
		seeker.StartPath( transform.position, target.position, OnPathComplete );

	public void GoToNewTarget(Transform newTarget) {
		//path = null;
		currentWaypoint = 0;
		nextWaypointDistance = 0.02f;
		target = newTarget;
		seeker = GetComponent<Seeker>();
		seeker.StartPath( transform.position, target.position, OnPathComplete );

	public void OnPathComplete ( Path p )
		Debug.Log( "Yay, we got a path back. Did it have an error? " + p.error );
		if (!p.error)
			path = p;
			//Reset the waypoint counter
			currentWaypoint = 0;

	public void Update ()
		if (path == null)
			//We have no path to move after yet

		if (currentWaypoint >= path.vectorPath.Count)
			Debug.Log( "End Of Path Reached" );

		//this.GetComponent<Rigidbody2D> ().MovePosition (path.vectorPath[currentWaypoint]);
		//Debug.Log (path.vectorPath[currentWaypoint]);
		//Direction to the next waypoint
		Vector3 dir = ( path.vectorPath[ currentWaypoint ] - transform.position ).normalized;
		//GetComponent<Rigidbody2D> ().velocity = new Vector2 (dir.x * 3, dir.y * 3);
		//Vector3.MoveTowards(transform.position, path.vectorPath[ currentWaypoint ], 2*Time.fixedDeltaTime);
		dir *= speed* Time.deltaTime;
		rb.velocity = dir;
		//this.gameObject.transform.Translate( dir );

		//Check if we are close enough to the next waypoint
		//If we are, proceed to follow the next waypoint	
		if (Vector3.Distance (transform.position, path.vectorPath [currentWaypoint]) < nextWaypointDistance) {

//use to switch between force types

public ForceMode2D fMode;

Vector3 direction = (path.vectorPath[currentWaypoint] - transform.position).normalized;

direction *= speed * Time.fixedDeltaTime;

//move the AI

rb.AddForce (direction, fMode);