Update dependency sass-loader to v7.3.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
sass-loader	dependencies	minor	7.2.0 -> 7.3.1

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Release Notes

webpack-contrib/sass-loader

### [`v7.3.1`](https://togithub.com/webpack-contrib/sass-loader/blob/master/CHANGELOG.md#​731httpsgithubcomwebpack-contribsass-loadercomparev730v731-2019-08-20) [Compare Source](https://togithub.com/webpack-contrib/sass-loader/compare/v7.3.0...v7.3.1) ### [`v7.3.0`](https://togithub.com/webpack-contrib/sass-loader/blob/master/CHANGELOG.md#​730httpsgithubcomwebpack-contribsass-loadercomparev720v730-2019-08-20) [Compare Source](https://togithub.com/webpack-contrib/sass-loader/compare/v7.2.0...v7.3.0) ##### Bug Fixes - handle module import ending `/` as module ([#​728](https://togithub.com/webpack-contrib/sass-loader/issues/728)) ([997a255](https://togithub.com/webpack-contrib/sass-loader/commit/997a255)) - resolution algorithm ([#​720](https://togithub.com/webpack-contrib/sass-loader/issues/720)) ([0e94940](https://togithub.com/webpack-contrib/sass-loader/commit/0e94940)) - use "compressed" output when mode is "production" ([#​723](https://togithub.com/webpack-contrib/sass-loader/issues/723)) ([b2af379](https://togithub.com/webpack-contrib/sass-loader/commit/b2af379)) ##### Features - `webpackImporter` option ([#​732](https://togithub.com/webpack-contrib/sass-loader/issues/732)) ([6f4ea37](https://togithub.com/webpack-contrib/sass-loader/commit/6f4ea37))

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