chore(deps-dev): bump webpack from 2.1.0-beta.21 to 5.31.2

Bumps [webpack](https://github.com/webpack/webpack) from 2.1.0-beta.21 to 5.31.2.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](webpack/webpack@v2.1.0-beta.21...v5.31.2)

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