Database access in data migrations defaults to the 'default' database. Force it to the user selected database instead.

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

mayan/apps/documents/migrations/0013_document_is_stub.py

@@ -7,7 +7,7 @@ from django.db import models, migrations
 def make_existing_documents_not_stubs(apps, schema_editor):
     Document = apps.get_model('documents', 'Document')
 
-    for document in Document.objects.all():
+    for document in Document.objects.using(schema_editor.connection.alias).all():
         document.is_stub = False
         document.save()