Bumps [webpacker](https://github.com/rails/webpacker) from 3.5.5 to 4.0.2.
- [Release notes](https://github.com/rails/webpacker/releases)
- [Changelog](https://github.com/rails/webpacker/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rails/webpacker/compare/v3.5.5...v4.0.2)

Signed-off-by: dependabot[bot] <support@dependabot.com>
Co-authored-by: Yamagishi Kazutoshi <ykzts@desire.sh>

* fix non-escaped html in the profile settings

* provide a default profile text in case if there's no custom one

* update haml syntax

* simplify default profile name to username

* sanitize user-input html but display emojified icons

* Add separate setting for sidebar text (site_short_description)

* Fix tests

* add haml_lint to Gemfile

* add .haml-lint.yml

* fix warnings of haml_lint

* Add flashes partial to DRY up admin/auth layouts

* Further consolidate flash messages

registration API