keyForCollection(modelName) {
    return this._container.inflector.pluralize(this.keyForModel(modelName));
  }
Used to customize the key when serializing a primary collection. By default this pluralizes the return value of `keyForModel`.

    For example, by default the following request may look like:

    ```
    GET /blogPosts

    {
      blogPosts: [
        {
          id: 1,
          title: 'Lorem ipsum'
        },
        ...
      ]
    }
    ```

    If your API hyphenates keys, you could overwrite `keyForCollection`:

    ```js
    // serializers/application.js
    export default Serializer.extend({
      keyForCollection(modelName) {
        return this._container.inflector.pluralize(dasherize(modelName));
      }
    });
    ```

    Now the response would look like:

    ```
    {
      'blog-posts': [
        {
          id: 1,
          title: 'Lorem ipsum'
        },
        ...
      ]
    }
    ```

    @method keyForCollection
    @param modelName
    @public