Remove version property from compose file (#20)

According to the Docker Compose specs, the version property is obsolete.

"The top-level version property is defined by the Compose Specification
for backward compatibility. It is only informative you'll receive
a warning message that it is obsolete if used.
Compose doesn't use version to select an exact schema to validate the
Compose file, but prefers the most recent schema when it's implemented."

See: https://github.com/compose-spec/compose-spec/blob/main/spec.md#version-top-level-element-obsolete

Closes gh-20

docker-compose.yml

@@ -1,4 +1,3 @@
-version: '3'
 services:
     mysql:
         container_name: mysql