server_config.tform: changed enable_spdy default to n

see:
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_448

interface/web/admin/form/server_config.tform.php

@@ -1024,7 +1024,7 @@ $form["tabs"]['web'] = array(
 		'enable_spdy' => array (
 			'datatype' => 'VARCHAR',
 			'formtype' => 'CHECKBOX',
-			'default'  => 'y',
+			'default'  => 'n',
 			'value' => array (
 				0 => 'n',
 				1 => 'y'