Fix examples in cleanup's README.md
Flag is `--hours-to-keep-clusters`, not `--days-to-keep-clusters`.
@@ -40,14 +40,14 @@ This command deletes test images older than 90 days and test clusters created
more than 24 hours ago in all Boskos projects.
```sh
-$ ./cleanup.sh --project-resource-yaml ci/prow/boskos_resources.yaml --days-to-keep-images 90 --days-to-keep-clusters 24`
+$ ./cleanup.sh --project-resource-yaml ci/prow/boskos_resources.yaml --days-to-keep-images 90 --hours-to-keep-clusters 24`
```
This command deletes test images older than 1 day and test clusters created
more than 24 hours ago in a personal project called `my-knative-project`.
```sh
-$ ./cleanup.sh --project my-knative-project --days-to-keep-images 1 --days-to-keep-clusters 24`
+$ ./cleanup.sh --project my-knative-project --days-to-keep-images 1 --hours-to-keep-clusters 24`
```
## Prow Job
