remove mini-css-extract-plugin from example webpack configuration

[sportshead]

fixes #65

This PR contains a:

• [ ] bugfix
• [ ] new feature
• [ ] code refactor
• [ ] test update
• [x] typo fix
• [ ] metadata update

Motivation / Use-Case

Makes things less confusing #65

Breaking Changes

None.

Additional Info

[sportshead]

mini-css-extract-plugin is not required to working with this plugin

So are you saying it is required or not?

[alexander-akait]

It is required when you want to extract CSS, but you can copy CSS files using copy-webpack-plugin (just one example)

[sportshead]

So it is not required for this plugin to function

[codecov[bot]]

Codecov Report

Merging #70 (6618980) into master (8865423) will increase coverage by 9.28%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #70      +/-   ##
==========================================
+ Coverage   90.21%   99.50%   +9.28%     
==========================================
  Files           5        3       -2     
  Lines         276      200      -76     
  Branches      100       67      -33     
==========================================
- Hits          249      199      -50     
+ Misses         25        1      -24     
+ Partials        2        0       -2     

Impacted Files	Coverage Δ
src/cjs.js	100.00% <0.00%> (ø)
src/Webpack5Cache.js
src/Webpack4Cache.js
src/index.js	100.00% <0.00%> (+3.24%)	:arrow_up:
src/minify.js	93.33% <0.00%> (+38.01%)	:arrow_up:

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[alexander-akait]

Yes, but popular usage with mini-css-extract-plugin, let's add comment about it, no need to remove