How to set rke etcd snapshots

NOW, my rke verion is v1.3.7. However, when I run

./rke_linux-amd64 config --name cluster.yml.

The config of cluster.yml is like as follow:
services:
etcd:

snapshot: “”
creation: “”
retention: “”

otherwise, It is below rke0.2 config.
why??

More, the backup is not use?? what the correctly config is ?