title: add_experimental_option() missing 1 required positional argument: 'value'
body: <p>I used the following code according to this post <a href="https://stackoverflow.com/questions/15165593/set-chrome-prefs-with-python-binding-for-selenium-in-chromedriver">Set chrome.prefs with python binding for selenium in chromedriver</a></p>
  
  <pre><code>chroptions = webdriver.ChromeOptions
  
  chroptions.add_experimental_option('prefs',{'download.default_directory' : 'C:\\Users\\elek2'})
  
  browser = webdriver.Chrome(executable_path ='C:\\Users\\elek2\\AppData\\Local\\chromedriver.exe', chrome_options = chroptions)
  </code></pre>
  
  <p>and I get this error: </p>
  
  <pre><code>TypeError: add_experimental_option() missing 1 required positional argument: 'value' 
  </code></pre>
  
  <p>What am I doing wrong... </p>