Update cron-job.yml

This change fixes this issue:

```
kapp: Error: Expected to find kind 'batch/v1beta1/CronJob', but did not:
- Kubernetes API server did not have matching apiVersion + kind
- No matching CRD was found in given configuration
```

Signed-off-by: John Cudd <[email protected]>

examples/jobs/cron-job.yml

@@ -1,4 +1,4 @@
-apiVersion: batch/v1beta1
+apiVersion: batch/v1
 kind: CronJob
 metadata:
   name: cron-job