Update dependency grunt-sass to v3

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
grunt-sass	devDependencies	major	2.0.0 -> 3.1.0

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Release Notes

sindresorhus/grunt-sass

### [`v3.1.0`](https://togithub.com/sindresorhus/grunt-sass/releases/v3.1.0) [Compare Source](https://togithub.com/sindresorhus/grunt-sass/compare/v3.0.2...v3.1.0) - Improve Sass error output ([#​296](https://togithub.com/sindresorhus/grunt-sass/issues/296)) [`08df45d`](https://togithub.com/sindresorhus/grunt-sass/commit/08df45d) ### [`v3.0.2`](https://togithub.com/sindresorhus/grunt-sass/compare/v3.0.1...v3.0.2) [Compare Source](https://togithub.com/sindresorhus/grunt-sass/compare/v3.0.1...v3.0.2) ### [`v3.0.1`](https://togithub.com/sindresorhus/grunt-sass/compare/v3.0.0...v3.0.1) [Compare Source](https://togithub.com/sindresorhus/grunt-sass/compare/v3.0.0...v3.0.1) ### [`v3.0.0`](https://togithub.com/sindresorhus/grunt-sass/releases/v3.0.0) [Compare Source](https://togithub.com/sindresorhus/grunt-sass/compare/v2.1.0...v3.0.0) This release requires Node.js 8 or later. You now have to choose whether you want `node-sass` or `dart-sass` by installing one of them yourself and setting it in the options. See the updated docs: Don't forget `const sass = require('node-sass')` or `const sass = require('dart-sass')`. ### [`v2.1.0`](https://togithub.com/sindresorhus/grunt-sass/compare/v2.0.0...v2.1.0) [Compare Source](https://togithub.com/sindresorhus/grunt-sass/compare/v2.0.0...v2.1.0)

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