Remove node 13 tests; change 12.16 to latest 12.x.x

[cspotcode]

Implements #1137

[codecov]

Codecov Report

Merging #1148 (48fc390) into master (48fc390) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1148   +/-   ##
=======================================
  Coverage   79.60%   79.60%           
=======================================
  Files           7        7           
  Lines         711      711           
  Branches      158      158           
=======================================
  Hits          566      566           
  Misses         89       89           
  Partials       56       56           

Flag	Coverage Δ
node_10	76.11% <0.00%> (ø)
node_12_15	76.46% <0.00%> (ø)
node_12_16	76.46% <0.00%> (ø)
node_13	78.90% <0.00%> (ø)
node_14	78.90% <0.00%> (ø)
node_14_13_0	78.05% <0.00%> (ø)
node_15	78.90% <0.00%> (ø)
typescript_2_7	78.90% <0.00%> (ø)
typescript_latest	78.05% <0.00%> (ø)
typescript_next	78.05% <0.00%> (ø)
ubuntu	78.76% <0.00%> (ø)
windows	78.90% <0.00%> (ø)

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[coveralls]

Coverage remained the same at 87.097% when pulling c2f1abd on ab/shrink-test-matrix into 48fc390 on master.