Update dependency preload-webpack-plugin to v3.0.0-beta.4

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
preload-webpack-plugin	devDependencies	patch	3.0.0-beta.3 -> 3.0.0-beta.4

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Release Notes

googlechromelabs/preload-webpack-plugin

### [`v3.0.0-beta.4`](https://togithub.com/googlechromelabs/preload-webpack-plugin/compare/7905a9ce0b91e1ccb89bb360497dcc84d1c6997a...fa21468e74cf1632e73900b2d7b1e5ae4e052be2) [Compare Source](https://togithub.com/googlechromelabs/preload-webpack-plugin/compare/7905a9ce0b91e1ccb89bb360497dcc84d1c6997a...fa21468e74cf1632e73900b2d7b1e5ae4e052be2)

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