Correct the master servers

These IP addresses are used by the powerDNS as master, all three needs to be in here, there NOTIFY messages are send by one of the three.
diff --git a/docs/dns.md b/docs/dns.md
index 3e6bda5..a530fe8 100644
--- a/docs/dns.md
+++ b/docs/dns.md
@@ -25,7 +25,11 @@
         description: PowerDNS Server
         # MiniDNS Configuration options
         masters:
-          - host: minidns
+          - host: {{ hostvars['ctl1']['ansible_host'] }}
+            port: 5354
+          - host: {{ hostvars['ctl2']['ansible_host'] }}
+            port: 5354
+          - host: {{ hostvars['ctl3']['ansible_host'] }}
             port: 5354
         # PowerDNS Configuration options
         options: