doc/tutorial/kubernetes: update k8s version
Change-Id: I54f13715bb8c7f0c67a3bec85f57543ed27f22d0
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/9941
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>