code: function renderFile(file, config) {
    const options = Object.assign({file}, config);
  
    return new Promise((resolve, reject) => {
      sass.render(options, (err, result) => {
        if (err) {
          return reject(err);
        }
        resolve(result.css);
      });
    });
  }
docs: Renders a single sass file
  @param {!string} file
  @param {!object} config
  @return {!Promise.<string>} The resulting css