django-2.0: Pass string to reverse.

urlsafe_base64_encode returns bytes. These can safely be converted to
ascii encoding. If we pass bytes to reverse, the match fails.

zerver/forms.py

@@ -217,7 +217,7 @@ def save(self,
 
         if user is not None:
             token = token_generator.make_token(user)
-            uid = urlsafe_base64_encode(force_bytes(user.id))
+            uid = urlsafe_base64_encode(force_bytes(user.id)).decode('ascii')
             endpoint = reverse('django.contrib.auth.views.password_reset_confirm',
                                kwargs=dict(uidb64=uid, token=token))