Update dependency copy-webpack-plugin to v6.0.4

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
copy-webpack-plugin	devDependencies	patch	6.0.3 -> 6.0.4

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Release Notes

webpack-contrib/copy-webpack-plugin

### [`v6.0.4`](https://togithub.com/webpack-contrib/copy-webpack-plugin/blob/master/CHANGELOG.md#​604-httpsgithubcomwebpack-contribcopy-webpack-plugincomparev603v604-2020-08-29) [Compare Source](https://togithub.com/webpack-contrib/copy-webpack-plugin/compare/v6.0.3...v6.0.4)

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