Fix typo in group name

templates/iptables.conf.j2

@@ -105,7 +105,7 @@
 # IMAP
 -A OUTPUT -p tcp -m tcp --dport 993 -j ACCEPT
 {% endif %}
-{% if inventory_hostname in groups.nagios %}
+{% if inventory_hostname in groups.nagios_server %}
 # NRPE
 -A OUTPUT -p tcp -m tcp --dport 5666 -j ACCEPT
 {% endif %}