DOCS-4851 Minor update to Behavior for rs.stepDown.txt

Signed-off-by: kay <kay.kim@10gen.com>

Author: ravindk89

source/reference/method/rs.stepDown.txt

@@ -46,7 +46,7 @@ with the primary. The command will wait up to either 10 seconds or the
 ``catchUpSecs`` for a secondary to catch up.
 
 If no electable secondary meets this criterion by the waiting period,
-the primary does not step down and the command errors.
+the primary does not step down and the method throws an exception.
 
 Upon successful stepdown, :method:`rs.stepDown()` forces all
 clients currently connected to the database to disconnect. This helps