Bump webpack-cli from 3.1.1 to 3.1.2

Bumps [webpack-cli](https://github.com/webpack/webpack-cli) from 3.1.1 to 3.1.2.
- [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/compare/v3.1.1...v3.1.2

)

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