.document.source() 建议编辑

                    .document.source([callback])
                

module.exports = {
  'get page source': function (browser) {
     browser.document.source(function (result) {
       console.log('current page source:', result.value);
     });
  },

  'get page source using ES6 async/await': async function (browser) {
     const pageSource = await browser.document.source();
     console.log('current page source:', pageSource);
  }
};