fix typo

roles/custom/matrix-dynamic-dns/templates/ddclient.conf.j2

@@ -31,7 +31,7 @@ secretapikey={{ dynamic_dns_domain_configuration.secretapikey }}
 {% endif %}
 
 {% if 'rootdomain' in dynamic_dns_domain_configuration %}
-root_domain={{ dynamic_dns_domain_configuration.rootdomain }}
+root-domain={{ dynamic_dns_domain_configuration.rootdomain }}
 
 {% if 'provider' in dynamic_dns_domain_configuration %}
 server={{ dynamic_dns_domain_configuration.provider }}