Can't apply turtorial crd.yaml example,The CustomResourceDefinition "ephemeralvolumeclaims.zalando.org" is invalid

[tarjintor]

I am trying to run the turtorial https://kopf.readthedocs.io/en/latest/walkthrough/resources/
And when I
kubectl apply -f crd.yaml
then it goes wrong as

The CustomResourceDefinition "ephemeralvolumeclaims.zalando.org" is invalid: spec.versions: Invalid value: []apiextensions.CustomResourceDefinitionVersion{apiextensions.CustomResourceDefinitionVersion{Name:"v1", Served:true, Storage:true, Schema:(*apiextensions.CustomResourceValidation)(0xc01c503bc0), Subresources:(*apiextensions.CustomResourceSubresources)(nil), AdditionalPrinterColumns:[]apiextensions.CustomResourceColumnDefinition(nil)}}: per-version schemas may not all be set to identical values (top-level validation should be used instead)

my k8s version are:

ubuntu@k8s-master:~/k8s_operator$ kubectl version 
Client Version: version.Info{Major:"1", Minor:"15", GitVersion:"v1.15.1", GitCommit:"4485c6f18cee9a5d3c3b4e523bd27972b1b53892", GitTreeState:"clean", BuildDate:"2019-07-18T09:18:22Z", GoVersion:"go1.12.5", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"15", GitVersion:"v1.15.4", GitCommit:"67d2fcf276fcd9cf743ad4be9a9ef5828adc082f", GitTreeState:"clean", BuildDate:"2019-09-18T14:41:55Z", GoVersion:"go1.12.9", Compiler:"gc", Platform:"linux/amd64"}

[tarjintor]

I read the docs of k8s v1.15 and search some git issues,I change crd.yaml to

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: ephemeralvolumeclaims.zalando.org
spec:
  scope: Namespaced
  group: zalando.org
  names:
    kind: EphemeralVolumeClaim
    plural: ephemeralvolumeclaims
    singular: ephemeralvolumeclaim
    shortNames:
      - evcs
      - evc
  versions:
    - name: v1
      served: true
      storage: true
  validation:
    openAPIV3Schema:
      type: object
      properties:
        spec:
          type: object
          x-kubernetes-preserve-unknown-fields: true
        status:
          type: object
          x-kubernetes-preserve-unknown-fields: true

It is OK then.