Do not include "typing" lib in `install_requires` if Python 3.5+

From https://pypi.python.org/pypi/typing:

NOTE: in Python 3.5 and later, the typing module lives in the stdlib, and installing this package has NO EFFECT.

We should not force the install of typing for Python version 3.5 or later.

I’m suggesting the following change:

install_requires = ['six>=1.2']
if sys.version_info < (3, 5):
    install_requires.append('typing')

setup(
    [....]
    install_requires=install_requires,
    [....]
)

@trbs let me know what you think.

[hynek]

@luzfcb the most correct way is currently PEP 508 but the most compatible way appears to be the using extras_require. It strictly depends on how old pip/setuptools you want to support.

[trbs]

If there other (edge) cases where it still fails please reopen the issue.