Fix typo in demo.ipynb

[terrytangyuan]

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

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This change is 

[jinchihe]

/lgtm

[zhenghuiwang]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: zhenghuiwang

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[terrytangyuan]

/retest

[k8s-ci-robot]

@terrytangyuan: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
kubeflow-metadata-presubmit	69f8a4ac88a02b87a5770823cefb793d9c55da1c	link	/test kubeflow-metadata-presubmit

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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