fix pihole upgrade strategy

library/ix-dev/charts/pihole/upgrade_strategy

@@ -8,7 +8,7 @@ from catalog_update.upgrade_strategy import datetime_versioning
 def newer_mapping(image_tags):
     key = list(image_tags.keys())[0]
     tags = {t for t in image_tags[key]}
-    version = datetime_versioning(list(tags), '%Y-%m-%d')
+    version = datetime_versioning(list(tags), '%Y.%m.%d')
     if not version:
         return {}