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>

- Reduce time-to-digest from 20 to 7 days
- Fetch mentions starting from +1 day since last login
- Fix case when last login is more recent than last e-mail
- Do not render all mentions, only 40, but show number in subject
- Do not send digest to moved accounts
- Do send digest to silenced accounts

* Change mailer avatar url

* Use full_asset_url method

* Use PNG images in HTML e-mails

* Make webpack use URLs with host so fonts load inside HTML e-mails

Convert this back to a relative URL in the premailer CSS loader
since local requests are quicker

* Improve responsive design

* Add missing PNG icon

* Change image URL in mailer to full path

* Add application_mailer.view_profile localization.

* HTML e-mails for NotificationMailer (except digest)

* Add HTML template for digest

* Fix build

* Localize date in digest

* Cover NotificationMailer more

* Simplify render in mailer views

* Simplify render in about/more view

* Simplify render in accounts follow views

* Simplify render in recovery code views

* Simplify render in stream entry embed

* Simplify render in stream entries status partial

* Simplify render in authorize follow new view

Better initial state for unlisted/nsfw toggles

as well as formatting of content