use logging.critical, not logging.fatal

fatal is an undocumented alias for critical

example/aitf-data-for-run

@@ -162,7 +162,7 @@ def main():
                     os.symlink(src, dst)
 
     except csppfetch.DownloadsFailedException as e:
-        logging.fatal(str(e))
+        logging.critical(str(e))
         return 1
 
     if not args.keep_old: