Fix getting domain name in Getting Started with Knative App Deployment

[miosman]

Domain information is available in the route resource and not the the knative service. Updating sample command to reflect the change.

Environment GKE 1.11.7-gke.4, Knative 0.4.0

Fixes #297

Proposed Changes

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[miosman]

I signed it!

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[samodell]

Thanks @miosman ! This looks good, but can you resolve the conflicts?

[miosman]

@samodell I've fixed the conflict and update the second instance where ksvc is used to get the domain for consistency.

[sebgoa]

/ok-to-test

[samodell]

/approve
/lgtm

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This pull-request has been approved by: miosman, samodell

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