ScoreBoard.cs

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ScoreBoard : MonoBehaviour {
    public GameManager gameManager;
    private Text scoreText;

	// Use this for initialization
	void Start () {
        scoreText = GetComponentInChildren<Text>();
	}
	
	// Update is called once per frame
	void Update () {
        scoreText.text = "" + gameManager.score;	
	}
}