Update dependency uglifyjs-webpack-plugin to v2.2.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
uglifyjs-webpack-plugin	devDependencies	minor	2.1.3 -> 2.2.0

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Release Notes

webpack-contrib/uglifyjs-webpack-plugin

### [`v2.2.0`](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/blob/master/CHANGELOG.md#​220httpsgithubcomwebpack-contribuglifyjs-webpack-plugincomparev213v220-2019-07-31) [Compare Source](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/compare/v2.1.3...v2.2.0) ##### Features - generate higher quality SourceMaps ([#​408](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/issues/408)) ([b1df135](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/commit/b1df135)) ##### [2.1.3](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/compare/v2.1.2...v2.1.3) (2019-05-15) ##### Bug Fixes - disable parallel on WSL ([#​403](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/issues/403)) ([7619736](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/commit/7619736)) - fallback for cache directory ([#​401](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/issues/401)) ([d117827](https://togithub.com/webpack-contrib/uglifyjs-webpack-plugin/commit/d117827))

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