Bump webpack-manifest-plugin from 3.0.0 to 3.1.0 (#65)

Bumps [webpack-manifest-plugin](https://github.com/shellscape/webpack-manifest-plugin) from 3.0.0 to 3.1.0.
- [Release notes](https://github.com/shellscape/webpack-manifest-plugin/releases)
- [Commits](shellscape/webpack-manifest-plugin@v3.0.0...v3.1.0)

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Author: dependabot[bot]