Drop node 12

[mroderick]

This PR drops support for Node 12 and adds support for Node 18

See https://nodejs.org/en/about/releases/

[codecov]

Codecov Report

Merging #428 (3ba1cec) into main (486125b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #428   +/-   ##
=======================================
  Coverage   95.51%   95.51%           
=======================================
  Files           1        1           
  Lines         624      624           
=======================================
  Hits          596      596           
  Misses         28       28           

Flag	Coverage Δ
unit	95.51% <ø> (ø)

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