fix: bump engines field to Node.js>=12

[erezrokah]

Hello 👋

I noticed the engines field doesn't match the latest release https://github.com/SBoudrias/Inquirer.js/releases/tag/inquirer%408.0.0

[SBoudrias]

Oh right, thanks!

[codecov]

Codecov Report

Merging #1077 (f33277d) into master (869cd40) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1077   +/-   ##
=======================================
  Coverage   88.30%   88.30%           
=======================================
  Files           4        4           
  Lines         171      171           
  Branches       23       23           
=======================================
  Hits          151      151           
  Misses          1        1           
  Partials       19       19           

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