changed cost.py to conform to pep8

Fixed costs/cost.py as a part of #821
I don't see the file in the white list for docstrings. Are you referring to
testing/cost.py?

On Mon, Nov 3, 2014 at 2:44 PM, Frédéric Bastien <notifications@github.com>
wrote:

> In pylearn2/devtools/tests/test_format.py:
>
> > @@ -236,7 +236,6 @@
> >      "optimization/test_linear_cg.py",
> >      "optimization/linesearch.py",
> >      "costs/mlp/__init__.py",
> > -    "costs/cost.py",
>
> This file is at a second place in test_format.py. Remove it at that second
> place. Maybe this will cause tests in this file to fail. If so, also fix
> them.
>
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> <https://github.com/lisa-lab/pylearn2/pull/1203/files#r19758818>.
>