update to use argument

Author: savannahostrowski

Doc/library/argparse.rst

@@ -2125,8 +2125,8 @@ Parser defaults
 
    Note that defaults can be set at both the parser level using :meth:`set_defaults` 
    and at the argument level using :meth:`add_argument`. If both are provided for the
-   same attribute, the order of setting these defaults determines which one takes 
-   precedence. The last default set for an attribute is the one that is used:
+   same argument, the order of setting these defaults determines which one takes 
+   precedence. The last default set for an argument is the one that is used:
 
      >>> parser = argparse.ArgumentParser()
      >>> parser.add_argument('--foo', default='bar')