Update dependency mini-css-extract-plugin to ^0.12.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
mini-css-extract-plugin	dependencies	minor	^0.11.0 -> ^0.12.0

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Release Notes

webpack-contrib/mini-css-extract-plugin

### [`v0.12.0`](https://togithub.com/webpack-contrib/mini-css-extract-plugin/blob/master/CHANGELOG.md#​0120-httpsgithubcomwebpack-contribmini-css-extract-plugincomparev0113v0120-2020-10-07) [Compare Source](https://togithub.com/webpack-contrib/mini-css-extract-plugin/compare/v0.11.3...v0.12.0)

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