Adjust imports in test cases

Author: rayluo

tests/test_client.py

@@ -9,9 +9,8 @@
 
 import requests
 
-from oauth2cli.oauth2 import Client
-from oauth2cli.authcode import obtain_auth_code
-from oauth2cli.assertion import JwtSigner
+from msal.oauth2cli import Client, JwtSigner
+from msal.oauth2cli.authcode import obtain_auth_code
 from tests import unittest, Oauth2TestCase