Bump grunt-contrib-uglify in /searx/static/themes/simple

Bumps [grunt-contrib-uglify](https://github.com/gruntjs/grunt-contrib-uglify) from 5.1.0 to 5.2.1.
- [Release notes](https://github.com/gruntjs/grunt-contrib-uglify/releases)
- [Changelog](https://github.com/gruntjs/grunt-contrib-uglify/blob/main/CHANGELOG)
- [Commits](https://github.com/gruntjs/grunt-contrib-uglify/compare/v5.1.0...v5.2.1

)

---
updated-dependencies:
- dependency-name: grunt-contrib-uglify
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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