Remove nose from setup.cfg

[paolostivanin]

I ran the tests with python3 -m unittest2 discover and everything went fine, so I assume that those strings I'd like to remove with this PR are not really needed.

[berkerpeksag]

The problem with this approach is that we would need to change tox.ini to invoke either unittest or unittest2 depending on the Python version (we still support Python 2.7) So we use nose as a Python 2 and 3 compatible test runner for now.

Also, there are more places we need to update in order to run tests on Travis CI:

.gitignore:41:nosetests.xml
requirements-tox.txt:1:nose>=1.3.0
tox.ini:11:        coverage run {envbindir}/nosetests -v --nocapture {posargs}

[berkerpeksag]

Thank you for your PR! I've now replaced nose with pytest as part of PR #229.