Update copyright to match k8s docs site

[unrolled]

This PR is part of the larger docs clean up issue: #4338

As per a slack conversation, we are updating the copyright text to match kubernetes.io. I've added some screenshots of the new copyright in multiple responsive sizes below:

Small

Medium

Large

[k8s-ci-robot]

Hi @unrolled. Thanks for your PR.

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[KnVerey]

Thanks!
/lgtm
/ok-to-test
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: KnVerey, unrolled

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