Fix tests.

Test worked on first run and failed on the second run.
The reason for this is the reference to `__file__` in `test.py`.
The problem is that after the first run, `__file__` points to the `.pyc` file instead of the original `.py` file which makes `pep257` fail (because it requires the source).
Merge pull request #74 from Nurdok/fix-tests

Fix tests