feature(syntax): proper yml for firewall playbook

firewall.yml

@@ -1,6 +1,11 @@
+---
+
 - hosts: all:!baybay-ponay.mateu.be:!machinbox.mateu.be:!muse-HP-EliteBook-820-G2.home.arpa
+  gather_facts: true
+  gather_subset:
+    - network
   tasks: []
 - hosts: router
-  diff: yes
+  diff: true
   roles:
-      - firewall
+    - firewall