[skeleton] Do not exclude setup.py from flake8 check in tox.ini
The file is flake8 compliant, actually.
3.34 (UNRELEASED)
=================
New features
------------
* Various bits of a CubicWeb application configuration can be now be
overridden through environments variables matching configuration option
names prefixed by ``CW_`` (for instance ``CW_BASE_URL``).
* Cubes are now standard Python packages named as ``cubicweb_<cubename>``.
They are not anymore installed in ``<prefix>/share/cubicweb/cubes``. Their
discovery by CubicWeb is handled by a new setuptools entry point
``cubicweb.cubes``. A backward compatibility layer is kept for "legacy"
cubes.