Added missing language string to fix #4140

Author: Till Brehm

interface/web/sites/lib/lang/de_web_vhost_domain.lng

@@ -147,4 +147,5 @@ $wb['http_port_txt'] = 'HTTP Port';
 $wb['https_port_txt'] = 'HTTPS Port';
 $wb['http_port_error_regex'] = 'HTTP Port invalid.';
 $wb['https_port_error_regex'] = 'HTTPS Port invalid.';
+$wb['enable_pagespeed_txt'] = 'Enable PageSpeed';
 ?>

interface/web/sites/lib/lang/en_web_vhost_domain.lng

@@ -152,4 +152,5 @@ $wb['http_port_txt'] = 'HTTP Port';
 $wb['https_port_txt'] = 'HTTPS Port';
 $wb['http_port_error_regex'] = 'HTTP Port invalid.';
 $wb['https_port_error_regex'] = 'HTTPS Port invalid.';
+$wb['enable_pagespeed_txt'] = 'Enable PageSpeed';
 ?>