update gomod for sample-controller

[carmark]

fix #359

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[gaocegege]

Why do we need sampler controller?

[carmark]

// set up signals so we handle the first shutdown signal gracefully
stopCh := signals.SetupSignalHandler()

[terrytangyuan]

Is there a way to get rid of it? Feels a little weird to rely on it.

[gaocegege]

/lgtm

[terrytangyuan]

Merging for now to unblock the existing issue. Let's track the issue with sample controller separately.

/approve

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