The new version of pip won't support Python 3.2
and we will need to tweak our .travis.yml and
tox.ini in order to run tests on PyPy 3.
However, since we already removed Python 3.2
from Travis, I decided to remove PyPy 3 as well
(it still targets Python 3.2)
This way we can avoid code duplication.
Also, this change makes tests faster due to ignoring the sdist step
and adds Python 3.2, 3.4 and PyPy 3 to build matrix.