Bump decompress and gulp-imagemin

Bumps [decompress](https://github.com/kevva/decompress) to 4.2.1 and updates ancestor dependency [gulp-imagemin](https://github.com/sindresorhus/gulp-imagemin). These dependencies need to be updated together.


Updates `decompress` from 3.0.0 to 4.2.1
- [Release notes](https://github.com/kevva/decompress/releases)
- [Commits](kevva/decompress@v3.0.0...v4.2.1)

Updates `gulp-imagemin` from 4.1.0 to 8.0.0
- [Release notes](https://github.com/sindresorhus/gulp-imagemin/releases)
- [Commits](sindresorhus/gulp-imagemin@v4.1.0...v8.0.0)

---
updated-dependencies:
- dependency-name: decompress
  dependency-type: indirect
- dependency-name: gulp-imagemin
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]