如何升级到pytz 2016.10而不是最新版本2018.4？

Question

我需要在Linux上安装pytz 2016.10。错误地，我升级到了2018.4。我尝试了以下方法来解决问题，但没有一个工作：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class spherecast : MonoBehaviour
{
    Rigidbody rb;
    public List<GameObject> CurrentHitObjects = new List<GameObject>();

    //public GameObject curobject;

    public float radius;
    public float maxdist;
    public LayerMask layermask;
    public float velocity;
    public Time deltatime;
    public Vector3 previous;

    private Vector3 origin;
    private Vector3 direction;

    private float hitdist;

    // Use this for initialization
    void Start()
    {
        foreach (GameObject cur in CurrentHitObjects)
        {
            previous = cur.transform.position;
        }
    }

    // Update is called once per frame
    void Update()
    {
        origin = transform.position;
        direction = transform.forward;

        hitdist = maxdist;
        CurrentHitObjects.Clear();

        RaycastHit[] hits = Physics.SphereCastAll(origin, radius, direction, maxdist, layermask, QueryTriggerInteraction.UseGlobal);
        foreach (RaycastHit hit in hits)
        {
            Plane[] planes = GeometryUtility.CalculateFrustumPlanes(Camera.main);
            if (GeometryUtility.TestPlanesAABB(planes, hit.collider.bounds))
            {
                float angle = Vector3.Angle(transform.forward, hit.point.normalized);
                float degree = Mathf.Acos(angle) * Mathf.Rad2Deg;
                Vector3 pos = hit.point;
                Debug.Log(hit.collider.name + "position =" + pos);
                CurrentHitObjects.Add(hit.transform.gameObject);
                hitdist = hit.distance;
                Debug.Log(hit.transform.name + "Distance ="+ hitdist);
                Debug.Log(hit.collider.name + "Angle = " + angle);

                velocity = ((hit.transform.position - previous).magnitude) / Time.deltaTime;
                previous = hit.transform.position;
                Debug.Log(hit.transform.name + "Velocity =" + velocity);
            }
            else
            {
                return ;
            }
        }
    }

    private void OnDrawGizmosSelected()
    {
        Gizmos.color = Color.red;
        Debug.DrawLine(origin, origin + direction * hitdist);
        Gizmos.DrawWireSphere(origin + direction * hitdist, radius);
    }
}

我不确定pytz升级到特定版本所需的格式。