haproxy: fix template typo

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

roles/haproxy/templates/haproxy.cfg

@@ -496,6 +496,7 @@ frontend zabbix-frontend
 backend zabbix-backend
     balance hdr(appserver)
     server  zabbix.stg zabbix.stg:80 check inter 10s rise 1 fall 2
+{% endif %}
 #    option  httpchk GET /
 #    http-check expect status 200,401,302
 {% if env == "production" %}