build: move system and samples test from Node 10 to Node 12

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[codecov]

Codecov Report

Merging #503 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #503   +/-   ##
=======================================
  Coverage   95.40%   95.40%           
=======================================
  Files           7        7           
  Lines        1719     1719           
  Branches       99       99           
=======================================
  Hits         1640     1640           
  Misses         77       77           
  Partials        2        2           

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