Fix missing string for logging placeholder

[zachzhaozy]

In py/release.py, an info logging uses a placeholder, but no string matches that.

This PR completes that missing string.

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[zachzhaozy]

I signed it!

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[coveralls]

Coverage decreased (-0.08%) to 49.782% when pulling 009cc29 on AIIFIT:fix-missing-string-for-logging-placeholder into 2a22ad4 on kubeflow:master.

[gaocegege]

/ok-to-test
/lgtm

[gaocegege]

/approve

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[gaocegege]

@zacharyzhao
Thanks for your contribution!