Bump webpacker from 5.4.0 to 5.4.2
Bump webpacker from 5.4.0 to 5.4.2

Bumps [webpacker](https://github.com/rails/webpacker) from 5.4.0 to 5.4.2.
- [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/v5.4.0...v5.4.2)

---
updated-dependencies:
- dependency-name: webpacker
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
diowa/ruby2-rails5-bootstrap-heroku,diowa/ruby2-rails5-bootstrap-heroku,diowa/ruby2-rails5-bootstrap-heroku