fix: worker_threads is only available on Node 12

[JounQin]

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[changeset-bot]

🦋 Changeset detected

Latest commit: 842bafe

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
synckit	Patch

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[codecov]

Codecov Report

Merging #34 (842bafe) into main (d84e48e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #34   +/-   ##
=======================================
  Coverage   97.43%   97.43%           
=======================================
  Files           1        1           
  Lines          78       78           
  Branches       24       24           
=======================================
  Hits           76       76           
  Misses          2        2           

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