Update dependency terser-webpack-plugin to v1.4.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
terser-webpack-plugin	dependencies	minor	1.3.0 -> 1.4.1

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Release Notes

webpack-contrib/terser-webpack-plugin

### [`v1.4.1`](https://togithub.com/webpack-contrib/terser-webpack-plugin/blob/master/CHANGELOG.md#​141httpsgithubcomwebpack-contribterser-webpack-plugincomparev140v141-2019-07-31) [Compare Source](https://togithub.com/webpack-contrib/terser-webpack-plugin/compare/v1.4.0...v1.4.1) ### [`v1.4.0`](https://togithub.com/webpack-contrib/terser-webpack-plugin/blob/master/CHANGELOG.md#​140httpsgithubcomwebpack-contribterser-webpack-plugincomparev130v140-2019-07-31) [Compare Source](https://togithub.com/webpack-contrib/terser-webpack-plugin/compare/v1.3.0...v1.4.0) ##### Features - generate higher quality SourceMaps ([#​109](https://togithub.com/webpack-contrib/terser-webpack-plugin/issues/109)) ([9d777f0](https://togithub.com/webpack-contrib/terser-webpack-plugin/commit/9d777f0))

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