Add --coverage flag for jest runner

[KevinGrandon]

Fixes #68

[codecov]

Codecov Report

Merging #82 into master will decrease coverage by 0.09%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master      #82     +/-   ##
=========================================
- Coverage    67.5%   67.41%   -0.1%     
=========================================
  Files          69       69             
  Lines        1465     1467      +2     
  Branches      325      326      +1     
=========================================
  Hits          989      989             
- Misses        421      423      +2     
  Partials       55       55

Impacted Files	Coverage Δ
commands/test-app.js	40% <ø> (ø)	⬆️
build/test-app-runtime.js	6.81% <0%> (-0.33%)	⬇️

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[KevinGrandon]

!merge