Bump webpack-cli from 3.1.2 to 3.2.1

Bumps [webpack-cli](https://github.com/webpack/webpack-cli) from 3.1.2 to 3.2.1.
- [Release notes](https://github.com/webpack/webpack-cli/releases)
- [Changelog](https://github.com/webpack/webpack-cli/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack/webpack-cli/commits)

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

Author: dependabot-support