Bump gulp-imagemin from 6.0.0 to 6.1.0 in /arctic/static/arctic

Bumps [gulp-imagemin](https://github.com/sindresorhus/gulp-imagemin) from 6.0.0 to 6.1.0.
- [Release notes](https://github.com/sindresorhus/gulp-imagemin/releases)
- [Commits](sindresorhus/gulp-imagemin@v6.0.0...v6.1.0)

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