Make image URL explicit

Author: lvarin

docker-compose.yaml

@@ -37,15 +37,15 @@ services:
       - "5672:5672"
 
   mongodb:
-    image: mongo:3.2
+    image: docker.io/library/mongo:3.2
     restart: unless-stopped
     volumes:
       - ../data/cwl_wes/db:/data/db
     ports:
       - "27017:27017"
 
   flower:
-    image: mher/flower:0.9.7
+    image: docker.io/mher/flower:0.9.7
     restart: unless-stopped
     links:
       - wes-worker