Remove obsolete version field from docker-compose.yml

The version field is obsolete in Docker Compose v2+ and generates
a warning. Removing it to clean up the configuration.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

docker-compose.yml

@@ -1,5 +1,3 @@
-version: '3.8'
-
 services:
   gogs-mcp-server:
     build: