[chore] Upgrade Go version to v1.18

[tenzen-y]

What this PR does / why we need it: I upgraded Go version to v1.18.

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 #

Checklist:

• [ ] Docs included if any changes are user facing

[coveralls]

Coverage remained the same at 72.857% when pulling 8fd3613a52d89276697cc5efd64899f5d153cdf3 on tenzen-y:upgrade-go-version into 8d58b0a53e35bdea7c1442dc0500a7e3cfa05ad3 on kubeflow:master.

[anencore94]

Thanks for updates :)

/lgtm

[johnugeorge]

Thanks /approve

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: johnugeorge, tenzen-y

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[johnugeorge]

/lgtm