importlib_metadata not installable on Python < 3.6
Your install_requires defines zipp>=0.5
as dependency, but today zipp released a new version which drops support for Python 3.5.
When installing importlib_metadata the dependency resolver now tries to install the latest package from zipp, which requires Python 3.6 and fails with
ERROR: Package 'zipp' requires a different Python: 3.5.9 not in '>=3.6'