Fix branch name for ci-kubernetes-build

[nikhita]

This should make https://testgrid.k8s.io/sig-release-master-blocking#build-master green.
Relevant slack message - https://kubernetes.slack.com/archives/C2C40FMNF/p1557837677253500

xref #12516
/assign @Katharine

[idealhack]

thanks for looking into this

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 993eabd6f523cecdd83163b2f5d040a58e4cba77

[justaugustus]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: idealhack, justaugustus, nikhita

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• config/jobs/kubernetes/sig-release/OWNERS [justaugustus]

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[k8s-ci-robot]

@nikhita: Updated the job-config configmap in namespace default using the following files:

• key kubernetes-builds.yaml using file config/jobs/kubernetes/sig-release/kubernetes-builds.yaml

In response to this:

This should make https://testgrid.k8s.io/sig-release-master-blocking#build-master green.
Relevant slack message - https://kubernetes.slack.com/archives/C2C40FMNF/p1557837677253500

xref #12516
/assign @Katharine

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