Fix Elasticsearch tests on Django 2.0

Fixes #4137

wagtail/search/tests/elasticsearch_common_tests.py

@@ -105,7 +105,7 @@ class ElasticsearchCommonSearchBackendTests:
 
     def test_update_index_command_schema_only(self):
         management.call_command(
-            'update_index', backend_name=self.backend_name, schema_only=True, interactive=False, stdout=StringIO()
+            'update_index', backend_name=self.backend_name, schema_only=True, stdout=StringIO()
         )
 
         # This should not give any results