Fix compatibility with webpack@5

[alexander-akait]

This PR contains a:

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

Motivation / Use-Case

avoid deprecation

Breaking Changes

In theory yes, but only for webpack@5, but because webpack@5 is in beta, you need to update webpack to latest version

Additional Info

fixes #284, fixes #277

[codecov]

Codecov Report

Merging #286 into master will increase coverage by 0.47%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #286      +/-   ##
==========================================
+ Coverage   93.05%   93.52%   +0.47%     
==========================================
  Files           5        5              
  Lines         403      386      -17     
  Branches      154      151       -3     
==========================================
- Hits          375      361      -14     
+ Misses         27       24       -3     
  Partials        1        1              

Impacted Files	Coverage Δ
src/Webpack4Cache.js	100.00% <100.00%> (ø)
src/Webpack5Cache.js	100.00% <100.00%> (+9.67%)	⬆️
src/index.js	94.79% <100.00%> (+0.03%)	⬆️

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