fix python version classifier

[kmohrf]

Hi,

I wanted to use pypi2deb to easily convert this package into a deb package for debian and debian derivates. The problem is that pypi2deb relies on correct Python version classifiers to tell which package is compatible with what Python version and the default is Python 2.

I’m not really sure if this package supports Python 2.x. In case it does the version classifiers probably should be

Programming Language :: Python :: 2.7
Programming Language :: Python :: 3

In case Python 2.x is not supported it should just be

Programming Language :: Python :: 3 :: Only

I’d be very happy if you could fix the classifiers and publish a new release, so pypi2deb works correctly.

Thank you for your time and your work on this project!

[kmohrf]

ping @zeekay