Update @types/webpack requirement from 4.4.19 to 4.4.20 (#3515)
Update @types/webpack requirement from 4.4.19 to 4.4.20 (#3515)

Updates the requirements on [@types/webpack](https://github.com/DefinitelyTyped/DefinitelyTyped) to permit the latest version.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
syuilo/Misskey,syuilo/Misskey