Execute test scripts in incognito mode

[Sjain01]

@john-doherty - First of all thank you for this amazing library.

Although I had already asked this question via #76 since the suggestion in there is not working and I cannot re-open it, I opened a new issue.

As per the suggestion, adding incognito under runtime folder in chromeDriver.js is not working.

` 'use strict';

var chromedriver = require('chromedriver');
var selenium = require('selenium-webdriver');

/**

• Creates a Selenium WebDriver using Chrome as the browser

• @returns {ThenableWebDriver} selenium web driver
  */
  module.exports = function() {

  var driver = new selenium.Builder().withCapabilities({
  browserName: 'chrome',
  javascriptEnabled: true,
  acceptSslCerts: true,
  chromeOptions: {
  args: ['start-maximized', 'disable-extensions','incognito']
  },
  path: chromedriver.path
  }).build();

  driver.manage().window().maximize();

  return driver;
  };`