Deprecation warning, affects compatibility with Python 3.8

When running tests with pytest, I noticed some deprecation warnings popping up. It appears that starting in Python 3.8 we will start to see some issues.

/python3.7/site-packages/jsonschema/compat.py:6:
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 MutableMapping, Sequence  # noqa

[Julian]

That code isn’t present on any recent version of this library.

[kazz-s]

your problem is that you got 2 import mixed up

import operator
import sys


try:
    from collections import MutableMapping, Sequence  # noqa
except ImportError:
    from collections.abc import MutableMapping, Sequence  # noqa

you should use from collections.abc ... by default and then on error fall back to from collections ....

While from collections import MutableMapping works we will keep getting this warning.