Fix incorrect port mapping of 2368 and update to latest docker image version

[hong823]

Ghost's port is displayed as 8080 which is incorrect, port 2368 should be the correct port as there are URLs on the page that is redirecting to port 2368.

Example:

http://localhost:2368/author/ghost/

[tianon]

It's not "incorrect" so much as "intentionally using a different host port than the port inside the container" which is why the line in the YAML has two values (the first being the "outside port" and the second being the "inside port" which is the port Ghost/Node is listening on).

What we should probably do instead is add an example url environment variable (which is a commonly requested addition) pointing to the exposed port.