See https://github.com/stefanpenner/es6-promise/issues/100

```
[WDS] Warnings while compiling.
./vendor/assets/javascripts/es6-promise.auto.js
Module not found: Error: Can't resolve 'vertx' in
'/Users/eric/Documents/gitlab/gitlab-development-kit/gitlab/vendor/assets/javascripts'
 @ ./vendor/assets/javascripts/es6-promise.auto.js 140:16-26
 @ ./app/assets/javascripts/application.js
 @ multi (webpack)-dev-server/client?http://localhost:3808
./application.js
```