Merge branch 'fix-stale-read-createclassifications' into 'master'

Fix stale read in CreateClassifications

Closes #508

See merge request !1046

arkindex/documents/serializers/ml.py

@@ -425,6 +425,7 @@ class ClassificationsSerializer(serializers.Serializer):
         ml_classes = dict(
             MLClass
             .objects
+            .using('default')
             .filter(corpus_id=parent.corpus_id, name__in=ml_class_names)
             .values_list('name', 'id')
         )