Remove unnecessary files from npm

[alexnoz]

There're some unnecessary files (eslint, prettier, CI configs, etc) in node_modules/parcel-bundler after installation.
This PR removes them, leaving only what is needed.

[codecov-io]

Codecov Report

Merging #836 into master will increase coverage by 1.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #836      +/-   ##
==========================================
+ Coverage   91.46%   92.82%   +1.36%     
==========================================
  Files          68       68              
  Lines        3573     3235     -338     
==========================================
- Hits         3268     3003     -265     
+ Misses        305      232      -73

Impacted Files	Coverage Δ
src/worker.js	90.9% <0%> (-9.1%)	⬇️
src/transforms/uglify.js	87.5% <0%> (-4.81%)	⬇️
src/packagers/HTMLPackager.js	94.23% <0%> (-3.11%)	⬇️
src/utils/installPackage.js	91.3% <0%> (-2.35%)	⬇️
src/utils/PromiseQueue.js	96.15% <0%> (-2.29%)	⬇️
src/assets/StylusAsset.js	86.95% <0%> (-1.8%)	⬇️
src/packagers/RawPackager.js	95% <0%> (-1.16%)	⬇️
src/assets/HTMLAsset.js	96.7% <0%> (-1.15%)	⬇️
src/assets/JSONAsset.js	91.3% <0%> (-1.01%)	⬇️
src/transforms/postcss.js	95.45% <0%> (-0.91%)	⬇️
... and 24 more

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