[REFACTOR] fix incompatible code for django 2.2 and python 3

removed .method() method call because now urlsafe_base64_encode returns string not bytes
files:
    - new_rest_api/tests.py
    - new_rest_api/views.py

new_rest_api/tests.py

@@ -122,7 +122,7 @@ class UserTests(APITestCase):
 
     def test_activation_function(self):
         user = BisaGoUser.objects.get(phone_number='089892218567').user
-        uid = urlsafe_base64_encode(force_bytes(user.pk)).decode()
+        uid = urlsafe_base64_encode(force_bytes(user.pk))
         token = account_activation_token.make_token(user)
         url = reverse('activate', kwargs={'uidb64' : uid, 'token' : token})
         response = self.client.get(url)

new_rest_api/views.py

@@ -84,7 +84,7 @@ def register_user(request):
             message = render_to_string('acc_active_email.html', {
                 'user' : user,
                 'domain' : request.get_host,
-                'uid' : urlsafe_base64_encode(force_bytes(user.pk)).decode(),
+                'uid' : urlsafe_base64_encode(force_bytes(user.pk)),
                 'token' : account_activation_token.make_token(user),
             })
             mail = EmailMessage(mail_subject, message, to=[email])