Fix ABC import
Pytest shows the following error, that should be fixed
/home/r2d2m-lapi/.pyenv/versions/3.7.0/envs/fml49/lib/python3.7/site-packages/jwt/api_jwt.py:4: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working
from collections import Iterable, Mapping