Fixed typo in docs/ref/django-admin.txt.

docs/ref/django-admin.txt

@@ -1940,5 +1940,5 @@ Output redirection
 Note that you can redirect standard output and error streams as all commands
 support the ``stdout`` and ``stderr`` options. For example, you could write::
 
-    with open('/path/to/command_output') as f:
+    with open('/path/to/command_output', 'w') as f:
         management.call_command('dumpdata', stdout=f)