style(docker-compose.yml): use different style for specifying a list.

No code changes.

[ci skip]

Author: php-coder

docker/docker-compose.yml

@@ -4,5 +4,7 @@ services:
   web:
     build: ./
     image: mystamps:latest
-    cap_drop: [ "ALL" ]
-    ports: [ "8080:8080" ]
+    cap_drop:
+      - "ALL"
+    ports:
+      - "8080:8080"