Bump webpack-cli from 2.0.13 to 2.1.2

Bumps [webpack-cli](https://github.com/webpack/webpack-cli) from 2.0.13 to 2.1.2.
- [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