Fix deprecation warnings for Django 1.11 and Django 2.0.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/documents/tests/test_api.py

@@ -7,8 +7,8 @@ import time
 from json import loads
 
 from django.contrib.auth import get_user_model
-from django.core.urlresolvers import reverse
 from django.test import override_settings
+from django.urls import reverse
 from django.utils.encoding import force_text
 
 from django_downloadview import assert_download_response