selenium.common.exceptions.WebDriverException: Message: An unknown server-side error occurred while processing the command. Original error: chrome not reachable
  (Session info: chrome=71.0.3578.99)
  (Driver info: chromedriver=2.46.628411 (3324f4c8be9ff2f70a05a30ebc72ffb013e1a71e),platform=Mac OS X 10.14.4 x86_64