require(file) {
    let path = this.resolveSync(file);
    return require(path);
  }
Calls `require` on a given module from the context of the project. For
    instance, an addon may want to require a class from the root project's
    version of ember-cli.

    @public
    @method require
    @param  {String} file File path or module name
    @return {Object}      Imported module