MailNotification: Fix double mail ending

While apparently the plugin was working with most mail servers,
the double \r\n.\r\n at the end violates the spec and newer
OpenSMTP servers are rejecting this.

mailnotification/smtpclient.cpp

@@ -351,7 +351,7 @@ void SmtpClient::processServerResponse(int responseCode, const QString &response
         break;
     case StateBody:
         if (responseCode == 354) {
-            send(m_messageData + "\r\n.\r\n");
+            send(m_messageData);
             setState(StateQuit);
         } else {
             handleUnexpectedSmtpCode(responseCode, response);