chore(deps): update dependency null-loader to v4

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
null-loader	devDependencies	major	^3.0.0 -> ^4.0.0

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Release Notes

webpack-contrib/null-loader

### [`v4.0.0`](https://togithub.com/webpack-contrib/null-loader/blob/master/CHANGELOG.md#​400-httpsgithubcomwebpack-contribnull-loadercomparev300v400-2020-04-15) [Compare Source](https://togithub.com/webpack-contrib/null-loader/compare/v3.0.0...v4.0.0) ##### Bug Fixes - support `webpack@5` ##### ⚠ BREAKING CHANGES - minimum required Nodejs version is `10.13`

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