docs(website): upgrade Node.js version from 18 to 20 in GitHub/Travis workflow examples

[DanRoscigno]

Since Node v20 is the required minimum changing to 20 in the GitHub workflows and Travis.

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

Test Plan

Test links

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Related issues/PRs

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[slorber]

Thanks! missed those docs!