Modernizing ProcessExitCode plugin

[Blackbaud-BobbyEarl]

Fixes blackbaud/skyux2#755

[codecov-io]

Codecov Report

Merging #173 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #173   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          38     38           
  Lines         845    843    -2     
  Branches      113    113           
=====================================
- Hits          845    843    -2

Flag	Coverage Δ
#builder	100% <100%> (ø)	⬆️
#runtime	100% <ø> (ø)	⬆️
#srcapp	100% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
plugin/process-exit-code/index.js	100% <100%> (ø)	⬆️
config/webpack/common.webpack.config.js	100% <100%> (ø)	⬆️
config/webpack/test.webpack.config.js	100% <100%> (ø)	⬆️

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[Blackbaud-BobbyEarl]

I don't believe my changes have introduced a reduction in code coverage. Since I removed code that was previously covered, there is now a smaller total amount of code, but the amount uncovered stayed the same, meaning a smaller percentage of code is now covered.