Update dependency css-loader to v3.1.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
css-loader	dependencies	minor	3.0.0 -> 3.1.0

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Release Notes

webpack-contrib/css-loader

### [`v3.1.0`](https://togithub.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md#​310httpsgithubcomwebpack-contribcss-loadercomparev300v310-2019-07-18) [Compare Source](https://togithub.com/webpack-contrib/css-loader/compare/v3.0.0...v3.1.0) ##### Bug Fixes - converting all (including reserved and control) filesystem characters to `-` (it was regression in `3.0.0` version) ([#​972](https://togithub.com/webpack-contrib/css-loader/issues/972)) ([f51859b](https://togithub.com/webpack-contrib/css-loader/commit/f51859b)) - default context should be undefined instead of null ([#​965](https://togithub.com/webpack-contrib/css-loader/issues/965)) ([9c32885](https://togithub.com/webpack-contrib/css-loader/commit/9c32885)) ##### Features - allow `modules.getLocalIdent` to return a falsy value ([#​963](https://togithub.com/webpack-contrib/css-loader/issues/963)) ([9c3571c](https://togithub.com/webpack-contrib/css-loader/commit/9c3571c)) - improved validation error messages ([65e4fc0](https://togithub.com/webpack-contrib/css-loader/commit/65e4fc0))

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