Update config/webpacker.yml
Update config/webpacker.yml

See https://github.com/rails/webpacker/blob/master/docs/v4-upgrade.md

Signed-off-by: Kenji Okimoto <7a4b90a0a1e6fc688adec907898b6822ce215e6c@clear-code.com>

fluent/fluentd-ui,fluent/fluentd-ui,fluent/fluentd-ui