Fix import error.

Author: WaVEV

django_mongodb/features.py

@@ -377,7 +377,7 @@ def django_test_expected_failures(self):
         "QuerySet.distinct() is not supported.": {
             "aggregation.tests.AggregateTestCase.test_sum_distinct_aggregate",
             "lookup.tests.LookupTests.test_lookup_collision_distinct",
-            "ordering.tests.OrderingTests.test_orders_nulls_first_on_filtered_subquery"
+            "ordering.tests.OrderingTests.test_orders_nulls_first_on_filtered_subquery",
             "queries.tests.ExcludeTest17600.test_exclude_plain_distinct",
             "queries.tests.ExcludeTest17600.test_exclude_with_q_is_equal_to_plain_exclude",
             "queries.tests.ExcludeTest17600.test_exclude_with_q_object_distinct",