Aberrant Docker version in RancherOS

I’m in a kubernetes cluster manage by Rancher (vsphere cloud provider)
When I add node to my cluster, the correct version of RancherOS is deploy (1.54).
I use : https://releases.rancher.com/os/latest/rancheros-vmware.iso
But the default Docker version is 17.3.2 and not the 18.09.8 as mentioned in : https://github.com/rancher/os/releases/

I also tried to setup a version in my cloud-init file, but nothing change :
engine: docker-18.09.8

I can switch with the ros command : ros switch docker-18.09.8.
But not very nice when you have a lot of node to connect to.