Import deprecation warning from Python 3.7

[dcecile]

Running Lupa in Python 3.7, I noticed this deprecation warning:

.../lib/python3.7/site-packages/lupa/__init__.py:18: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working

I think it's this import from lupa/_lupa.pyx:

from collections import Mapping

Switching the import to collections.abc won't work for Python 2, so an extra check would be needed... (Six has an open issue)

[scoder]

Thanks, fixed in lupa 1.8.