keyForRelationship(modelName) {
    return camelize(this._container.inflector.pluralize(modelName));
  }
Use this hook to format the key for collections related to this model. *modelName* is the named parameter for the relationship.

    For example, if you're serializing an `author` that
    sideloads many `blogPosts`, the default response will look like:

    ```
    {
      author: {...},
      blogPosts: [...]
    }
    ```

    Overwrite `keyForRelationship` to format this key:

    ```js
    // serializers/application.js
    export default Serializer.extend({
      keyForRelationship(modelName) {
        return underscore(modelName);
      }
    });
    ```

    Now the response will look like this:

    ```
    {
      author: {...},
      blog_posts: [...]
    }
    ```

    @method keyForRelationship
    @param modelName
    @public