Updated docker-compose to remove obsolete version syntax (#692)

Removes `version:` syntax in `docker-compose` file. If left in, it
throws an obsolete warning. I removed it from the docker-compose file to
reduce unnecessary warnings and to keep the code up to current
standards.

See [Version top-level element
(obsolete)](https://docs.docker.com/compose/compose-file/04-version-and-name/#version-top-level-element-obsolete)
for reference.

docker-compose.yml

@@ -1,5 +1,3 @@
-version: '3.9'
-
 x-base_service: &base_service
     ports:
       - "${WEBUI_PORT:-7860}:7860"