Use docker-compose spec v3 in nginx receipt

Previously v1 was used.

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

docs/recipes/nginx.md

@@ -168,6 +168,9 @@ Review the [requirements](index.md#requirements), then follow these steps.
 5.  Create the compose file. Paste the following YAML into a new file called `docker-compose.yml`.
 
     ```yaml
+    version: "3"
+
+    services:
         nginx:
           # Note : Only nginx:alpine supports bcrypt.
           # If you don't need to use bcrypt, you can use a different tag.
@@ -175,8 +178,8 @@ Review the [requirements](index.md#requirements), then follow these steps.
           image: "nginx:alpine"
           ports:
             - 5043:443
-      links:
-        - registry:registry
+          depends_on:
+            - registry
           volumes:
             - ./auth:/etc/nginx/conf.d
             - ./auth/nginx.conf:/etc/nginx/nginx.conf:ro