HCL2 example of "windows_container": true uses ubuntu image

[mloskot]

On https://developer.hashicorp.com/packer/plugins/builders/docker#docker-for-windows this example does not use correct, does it?

[lbajolet-hashicorp]

Good catch @mloskot!

I'll open a PR to fix this, thanks for the report

[mloskot]

Thank you @lbajolet-hashicorp