correct the version of beta annotation for storage

[pacoxu]

https://github.com/kubernetes/kubernetes/blob/7a94debba5f8c21bbf8b42b2a7f1d5e974ddb837/CHANGELOG/CHANGELOG-1.9.md#storage-2

Before Kubernetes v1.6, this was done via the
volume.beta.kubernetes.io/storage-class annotation. However, this annotation
is deprecated since v1.9. Users now can and should instead use the
storageClassName field of the PersistentVolumeClaim object.

• 1.6: StorageClassName attribute has been added to PersistentVolume and PersistentVolumeClaim objects and should be used instead of annotation volume.beta.kubernetes.io/storage-class. The beta annotation is still working in this release, however it will be removed in a future release. (Remove obsolete references to 'kubeadm alpha kubeconfig' command #42128, @jsafrane)
• 1.9: The volume.beta.kubernetes.io/storage-class annotation is deprecated. It will be removed in a future release. For the StorageClass API object, use v1, and in place of the annotation use v1.PersistentVolumeClaim.Spec.StorageClassName and v1.PersistentVolume.Spec.StorageClassName instead. (#53580, @xiangpengzhao)

maybe removed later.

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[celestehorgan]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 9a081cde09afa5fb03cfd7088928a8d4299ef01d

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