Update dependency copy-webpack-plugin to v6.4.1

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
copy-webpack-plugin	6.4.0 -> 6.4.1

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Release Notes

webpack-contrib/copy-webpack-plugin

### [`v6.4.1`](https://togithub.com/webpack-contrib/copy-webpack-plugin/releases/v6.4.1) [Compare Source](https://togithub.com/webpack-contrib/copy-webpack-plugin/compare/v6.4.0...v6.4.1) ##### [6.4.1](https://togithub.com/webpack-contrib/copy-webpack-plugin/compare/v6.4.0...v6.4.1) (2020-12-16) ##### Bug Fixes - compatibility with webpack 4 file system ([#​570](https://togithub.com/webpack-contrib/copy-webpack-plugin/issues/570)) ([720026a](https://togithub.com/webpack-contrib/copy-webpack-plugin/commit/720026ad0c526e003ab7270f1712fd712d4fdfad))

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