[Notifications] Fix UnicodeEncodeError upon non-ascii torrent name

smtplib.SMTP.sendmail expects 'msg' in string of ascii chars or bytes,
where the former gets encoded to bytes through ascii codec, hence
raising said error, but now fixed by encoding to bytes ourself through
utf-8

Closes: https://github.com/deluge-torrent/deluge/pull/383

deluge/plugins/Notifications/deluge_notifications/core.py

@@ -148,7 +148,7 @@ Date: %(date)s
 
         try:
             try:
-                server.sendmail(self.config['smtp_from'], to_addrs, message)
+                server.sendmail(self.config['smtp_from'], to_addrs, message.encode())
             except smtplib.SMTPException as ex:
                 err_msg = (
                     _('There was an error sending the notification email: %s') % ex