Fix typo in INFO message related with rsync version

There's a typo in the INFO message sent when rsync prior to 3.1
is detected. The message has been written differently now to make
it clear to the user, fixing the typo at the same time.

Signed-off-by: Martín Marqués <martin.marques@enterprisedb.com>

barman/copy_controller.py

@@ -506,7 +506,7 @@ def _rsync_set_pre_31_mode(self):
         """
         _logger.info(
             "Detected rsync version less than 3.1. "
-            "top using '--ignore-missing-args' argument."
+            "Stopping use of '--ignore-missing-args' argument."
         )
         self.rsync_has_ignore_missing_args = False
         self.rsync_cache.clear()