Update dependency webpack-cli to v3.3.8

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
webpack-cli	devDependencies	patch	3.3.7 -> 3.3.8

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Release Notes

webpack/webpack-cli

### [`v3.3.8`](https://togithub.com/webpack/webpack-cli/releases/v3.3.8) [Compare Source](https://togithub.com/webpack/webpack-cli/compare/v3.3.7...v3.3.8) Webpack-CLI v3.3.8 comes with a validation bugfix to support webpack 5 and version 4. A full changelog is found [here](https://togithub.com/webpack/webpack-cli/blob/master/CHANGELOG.md#​338-2019-09-05)

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