Update en_mail_user_autoresponder.lng to have "Subject" instead of "Betreff" in English translation

Author: Techwolf12

interface/web/mailuser/lib/lang/en_mail_user_autoresponder.lng

@@ -9,5 +9,5 @@ $wb["autoresponder_end_date_txt"] = 'End by';
 $wb["autoresponder_end_date_isgreater"] = 'End date must be set and be later than start date.';
 $wb['autoresponder_active'] = 'Enable the autoresponder';
 $wb['now_txt']='Now';
-$wb['autoresponder_subject_txt'] = 'Betreff';
+$wb['autoresponder_subject_txt'] = 'Subject';
 ?>