Add quit logic to end the session

On BrowserStack it seems my sessions are staying open until
they time out.  That's making the tests take way too long.
This is an attempt to force them closed more quickly.

Author: craigfowler

CSF.Screenplay.Selenium/BrowseTheWeb.cs

@@ -83,6 +83,7 @@ protected virtual void Dispose(bool disposing)
             {
                 if (disposing)
                 {
+                    webDriverAndOptions?.WebDriver.Quit();
                     webDriverAndOptions?.Dispose();
                 }
                 disposedValue = true;