Do not apply new-module-imports rule to an addon's app folder

When updating addons to use the new modules syntax we have to avoid updating any files in the addon's `app/` directory since that is transpiled by the addon's consuming app which may not have an up-to-date version of ember-cli-babel. With this addon installed though eslint will fail any files in the app directory that violate this rule. I added a one file exception to the affected file in my addon for now, but I'm not sure if there's a better way to handle this.