Bump grunt-contrib-imagemin from 3.0.0 to 4.0.0 in the dev-grunt group

Bumps the dev-grunt group with 1 update: [grunt-contrib-imagemin](https://github.com/gruntjs/grunt-contrib-imagemin).


Updates `grunt-contrib-imagemin` from 3.0.0 to 4.0.0
- [Release notes](https://github.com/gruntjs/grunt-contrib-imagemin/releases)
- [Commits](gruntjs/grunt-contrib-imagemin@v3.0.0...v4.0.0)

---
updated-dependencies:
- dependency-name: grunt-contrib-imagemin
  dependency-type: direct:development
  update-type: version-update:semver-major
  dependency-group: dev-grunt
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]