use qualified hostnames for images stored on docker.io

docker/compose/docker-compose.portainer.yml

@@ -31,13 +31,13 @@
 version: "3.4"
 services:
   broker:
-    image: redis:6.0
+    image: docker.io/library/redis:6.0
     restart: unless-stopped
     volumes:
       - redisdata:/data
 
   db:
-    image: postgres:13
+    image: docker.io/library/postgres:13
     restart: unless-stopped
     volumes:
       - pgdata:/var/lib/postgresql/data