docs: function () {
      var screenshotsDir = path.join(process.env.CIRCLE_ARTIFACTS || '.', 'screenshots');
      if (!fs.existsSync(screenshotsDir)) {
        fs.mkdirSync(screenshotsDir);
      }
      return this
        .saveScreenshot(path.join(screenshotsDir, (new Date()).toString() + '.png'))
        .then(function (filePath) {
          console.log('saved screenshot to file', filePath);
        });
    }