Implemented #4978 Changing regex for dns_ns to allow delegating LE requests to seperate nameservers

Author: Till Brehm

interface/web/dns/form/dns_ns.tform.php

@@ -86,7 +86,7 @@
 					'type' => 'TOLOWER')
 			),
 			'validators' => array (  0 => array ( 'type' => 'REGEX',
-					'regex' => '/^[a-zA-Z0-9\.\-]{0,255}$/',
+					'regex' => '/^[_a-zA-Z0-9\.\-]{0,255}$/',
 					'errmsg'=> 'name_error_regex'),
 			),
 			'default' => '',