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>

* Update better_errors to version 2.4.0

* Update binding_of_caller to version 0.7.3

* Update bootsnap to version 1.1.5

* Update browser to version 2.5.2

* Update capistrano to version 3.10.0

* Update capistrano-bundler to version 1.3.0

* Update capistrano-rbenv to version 2.1.2

* Update capybara to version 2.15.4

* Update cld3 to version 3.2.1

* Update fabrication to version 2.18.0

* Update fog-openstack to version 0.1.22

* Update kaminari to version 1.1.1

* Update lograge to version 0.7.1

* Update nokogiri to version 1.8.1

* Update oj to version 3.3.9

* Update ox to version 2.8.1

* Update parallel_tests to version 2.17.0

* Update pkg-config to version 1.2.8

* Update rspec-rails to version 3.7.1

* Update rubocop to version 0.51.0

* Update scss_lint to version 0.55.0

* Update sidekiq to version 5.0.5

* Update sidekiq-scheduler to version 2.1.10

* Update tzinfo-data to version 1.2017.3

* Update webpacker to version 3.0.2

* bundle update

* Replace browserify with webpack

* Add react-intl-translations-manager

* Do not minify in development, add offline-plugin for ServiceWorker background cache updates

* Adjust tests and dependencies

* Fix production deployments

* Fix tests

* More optimizations

* Improve travis cache for npm stuff

* Re-run travis

* Add back support for custom.scss as before

* Remove offline-plugin and babili

* Fix issue with Immutable.List().unshift(...values) not working as expected

* Make travis load schema instead of running all migrations in sequence

* Fix missing React import in WarningContainer. Optimize rendering performance by using ImmutablePureComponent instead of
React.PureComponent. ImmutablePureComponent uses Immutable.is() to compare props. Replace dynamic callback bindings in
<UI />

* Add react definitions to places that use JSX

* Add Procfile.dev for running rails, webpack and streaming API at the same time