docs: Update cron-backfill.yaml: regexpr has been fixed (argoproj#14376)

Signed-off-by: Andrey Kuznetsov <[email protected]>
Co-authored-by: Alan Clucas <[email protected]>

Author: 2 people

examples/cron-backfill.yaml

@@ -117,4 +117,4 @@ spec:
               # run for the 19th to the 21st
               start: "19"
               end: "21"
-              format: "2020-05-%02X"
+              format: "2020-05-%02d"