Update less requirement to ^3.8.0 in /{{cookiecutter.app_name}}

Updates the requirements on [less](https://github.com/less/less.js) to permit the latest version.
- [Release notes](https://github.com/less/less.js/releases)
- [Changelog](https://github.com/less/less.js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/less/less.js/commits/v3.8.0

)

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