fix: support Node >=10

[NMinhNguyen]

This is a follow-up to #459.

What: support older Node 10 versions

Why: to make the upgrade easier since there doesn't appear to be a hard requirement to use Node 10.18 (see #459 (comment)).

How: changed engines.node from >=10.18 to >=10.

Checklist:

• Documentation added to the
  docs site
• I've prepared a PR for types targeting
  DefinitelyTyped
• Tests
• Ready to be merged
  

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[codecov]

Codecov Report

Merging #465 into beta will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff         @@
##           beta   #465   +/-   ##
===================================
  Coverage   100%   100%           
===================================
  Files        22     22           
  Lines       420    420           
  Branches    100    100           
===================================
  Hits        420    420

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[kentcdodds]

Thank you!

[kentcdodds]

@all-contributors please add @NMinhNguyen for code

[allcontributors]

@kentcdodds

I've put up a pull request to add @NMinhNguyen! 🎉