Bump webpack from 4.19.1 to 4.20.0

Bumps [webpack](https://github.com/webpack/webpack) from 4.19.1 to 4.20.0.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](https://github.com/webpack/webpack/compare/v4.19.1...v4.20.0

)

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