Bump gulp-sass from 3.2.1 to 4.0.2 in /arctic/static/arctic

Bumps [gulp-sass](https://github.com/dlmanning/gulp-sass) from 3.2.1 to 4.0.2.
- [Release notes](https://github.com/dlmanning/gulp-sass/releases)
- [Changelog](https://github.com/dlmanning/gulp-sass/blob/master/CHANGELOG.md)
- [Commits](dlmanning/gulp-sass@v3.2.1...v4.0.2)

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