Fix path default-http-backend.yaml

[atotto]

I get the following error:

sed: can't read default-http-backend.yaml: No such file or directory

Thanks.

[k8s-ci-robot]

Hi @atotto. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[rramkumar1]

/lgtm
/assign @nicksardo