bump mark-example to 2.2.0

docker-compose.yml

 version: '2.0'
 services:
   mark:
-    image: cylab/mark-example:1.5.1
+    image: cylab/mark-example:2.2.0
     environment:
     - MARK_MONGO_HOST=mark-web_mongo_1
     ports:
     - "8080:8080"
-    links:
+    depends_on:
     - mongo
   mongo:
     image: mongo:4.4