[docs] Small issue in argparse module docs

[Dmitry Medvinsky]

Hello, folks.

I've noticed a small issue in the last example in the Action section
of argparse module documentation. Here's the link:

http://docs.python.org/library/argparse.html#action

There is wrong indentation in the definition of the __call__ method of
FooAction class. Not a big deal, but anyway.