fix: cache for extracted comments

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

partial #312, need investigate why comments not extracted (maybe terser regression)

Breaking Changes

No

Additional Info

No

[codecov]

Codecov Report

Merging #314 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #314      +/-   ##
==========================================
+ Coverage   98.51%   98.53%   +0.01%     
==========================================
  Files           5        5              
  Lines         404      409       +5     
  Branches      161      163       +2     
==========================================
+ Hits          398      403       +5     
  Misses          6        6              

Impacted Files	Coverage Δ
src/Webpack4Cache.js	100.00% <100.00%> (ø)
src/index.js	97.71% <100.00%> (+0.01%)	⬆️

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