use new unittest.mock from standard library

tests/requirements.txt

@@ -1,5 +1,4 @@
 Sphinx>=1.8.0
-mock
 pytest
 pytest-cov
 aiounittest

tests/unit/http/test_async_http_client.py

@@ -1,7 +1,7 @@
 import aiounittest
+from unittest.mock import patch, AsyncMock
 
 from aiohttp import ClientSession
-from mock import patch, AsyncMock
 from twilio.http.async_http_client import AsyncTwilioHttpClient
 
 

tests/unit/http/test_http_client.py

@@ -2,8 +2,8 @@
 import os
 import unittest
 from collections import OrderedDict
+from unittest.mock import Mock, patch
 
-from mock import Mock, patch
 from requests import Session
 
 from twilio.base.exceptions import TwilioRestException

tests/unit/http/test_validation_client.py

@@ -1,8 +1,8 @@
 # -*- coding: utf-8 -*-
 
 import unittest
+from unittest.mock import patch, Mock
 
-from mock import patch, Mock
 from requests import Request
 from requests import Session
 

tests/unit/jwt/test_jwt.py

@@ -1,8 +1,8 @@
 import time as real_time
 import unittest
+from unittest.mock import patch
 
 import jwt as jwt_lib
-from mock import patch
 
 from twilio.jwt import Jwt, JwtDecodeError
 

tests/unit/rest/test_client.py

@@ -1,7 +1,7 @@
 import unittest
 import aiounittest
+from unittest.mock import AsyncMock, Mock
 
-from mock import AsyncMock, Mock
 from twilio.http.response import Response
 from twilio.rest import Client