docs: update required version of Nodejs from 10.0 to 14.17.5 in README.md

[xupea]

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• The changes are appropriately documented (if applicable).
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[welcome]

Thanks for opening a pull request!

Here are some highlighted action items that will help get it across the finish line, from the
pull request guidelines:

• Follow the JavaScript coding style.
• Run npm run lint locally to catch formatting errors earlier.
• Document any user-facing changes in NEWS.md and other docs.
• Include tests when adding/changing behavior.

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[erickzhao]

LGTM! Thank you for the contribution.

[welcome]

Thanks for your contribution! 🎉