[docs] Selenium image is incorrect in WebDriver wiki page

WebDriver wiki documentation requires updating.

**URL:** https://github.com/dgtlmoon/changedetection.io/wiki/Fetching-pages-with-WebDriver

**Issue:** The `selenium/standalone-chrome-debug` image is now deprecated and the specific version listed on this wiki page (`selenium/standalone-chrome-debug:4`) is no longer available. This results in docker failing with "docker: Error response from daemon: manifest for selenium/standalone-chrome-debug:4 not found: manifest unknown: manifest unknown."

**Fix:** Simply changing this to `selenium/standalone-chrome-debug` (removing the `:4` from the end) will make this work, but it does mean that the deprecated selenium image will be used.

Does this work with the standalone-chrome image: https://hub.docker.com/r/selenium/standalone-chrome ?