Update dependency terser-webpack-plugin to v2.1.2

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
terser-webpack-plugin	dependencies	patch	2.1.0 -> 2.1.2

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Release Notes

webpack-contrib/terser-webpack-plugin

### [`v2.1.2`](https://togithub.com/webpack-contrib/terser-webpack-plugin/blob/master/CHANGELOG.md#​212httpsgithubcomwebpack-contribterser-webpack-plugincomparev211v212-2019-09-28) [Compare Source](https://togithub.com/webpack-contrib/terser-webpack-plugin/compare/v2.1.1...v2.1.2) ### [`v2.1.1`](https://togithub.com/webpack-contrib/terser-webpack-plugin/blob/master/CHANGELOG.md#​212httpsgithubcomwebpack-contribterser-webpack-plugincomparev211v212-2019-09-28) [Compare Source](https://togithub.com/webpack-contrib/terser-webpack-plugin/compare/v2.1.0...v2.1.1)

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