chore: remove obsolete version field from docker-compose.yml

Docker Compose v2+ no longer requires the version field. Removing it to avoid warnings.

docker-compose.yml

@@ -5,15 +5,13 @@
 #   2. Access at http://localhost:3000
 #
 # Using MySQL instead of PostgreSQL:
-#   1. Comment out the postgres service and SQL_DSN line 15
-#   2. Uncomment the mysql service and SQL_DSN line 16
-#   3. Uncomment mysql in depends_on (line 28)
-#   4. Uncomment mysql_data in volumes section (line 64)
+#   1. Comment out the postgres service and SQL_DSN line 13
+#   2. Uncomment the mysql service and SQL_DSN line 14
+#   3. Uncomment mysql in depends_on (line 26)
+#   4. Uncomment mysql_data in volumes section (line 62)
 #
 # ⚠️  IMPORTANT: Change all default passwords before deploying to production!
 
-version: '3.4' # For compatibility with older Docker versions
-
 services:
   new-api:
     image: calciumion/new-api:latest