tweak a listing, get tests passing again

Author: hjwp

appendix_django.asciidoc

@@ -104,12 +104,12 @@ but it is still made up of familiar-looking Django code:
 def test_repository_can_retrieve_a_batch_with_allocations():
     sku = "PONY-STATUE"
     d_line = django_models.OrderLine.objects.create(orderid="order1", sku=sku, qty=12)
-    d_b1 = django_models.Batch.objects.create(
-    reference="batch1", sku=sku, qty=100, eta=None
-)
-    d_b2 = django_models.Batch.objects.create(
-    reference="batch2", sku=sku, qty=100, eta=None
-)
+    d_batch1 = django_models.Batch.objects.create(
+        reference="batch1", sku=sku, qty=100, eta=None
+    )
+    d_batch2 = django_models.Batch.objects.create(
+        reference="batch2", sku=sku, qty=100, eta=None
+    )
     django_models.Allocation.objects.create(line=d_line, batch=d_batch1)
 
     repo = repository.DjangoRepository()