Bump node-sass and gulp-sass

Removes [node-sass](https://github.com/sass/node-sass). It's no longer used after updating ancestor dependency [gulp-sass](https://github.com/dlmanning/gulp-sass). These dependencies need to be updated together.


Removes `node-sass`

Updates `gulp-sass` from 3.2.1 to 5.1.0
- [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...v5.1.0)

---
updated-dependencies:
- dependency-name: node-sass
  dependency-type: indirect
- dependency-name: gulp-sass
  dependency-type: direct:development
...

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Author: dependabot[bot]