Update webpack requirement from 4.26.1 to 4.28.3 (#3822)
Update webpack requirement from 4.26.1 to 4.28.3 (#3822)

Updates the requirements on [webpack](https://github.com/webpack/webpack) to permit the latest version.
- [Release notes](https://github.com/webpack/webpack/releases)
- [Commits](https://github.com/webpack/webpack/commits/v4.28.3)

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