Bump tough-cookie, gulp-sass and node-sass

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


Removes `tough-cookie`

Updates `gulp-sass` from 4.1.1 to 6.0.1
- [Release notes](https://github.com/dlmanning/gulp-sass/releases)
- [Changelog](https://github.com/dlmanning/gulp-sass/blob/master/CHANGELOG.md)
- [Commits](dlmanning/gulp-sass@v4.1.1...v6.0.1)

Updates `node-sass` from 4.14.1 to 9.0.0
- [Release notes](https://github.com/sass/node-sass/releases)
- [Changelog](https://github.com/sass/node-sass/blob/master/CHANGELOG.md)
- [Commits](sass/node-sass@v4.14.1...v9.0.0)

---
updated-dependencies:
- dependency-name: tough-cookie
  dependency-version: 
  dependency-type: indirect
- dependency-name: gulp-sass
  dependency-version: 6.0.1
  dependency-type: direct:development
- dependency-name: node-sass
  dependency-version: 9.0.0
  dependency-type: direct:development
...

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Author: dependabot[bot]