Deprecation warning in renderers.py

[Yelinz]

.../python3.7/site-packages/rest_framework_json_api/renderers.py:5: 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, OrderedDict, defaultdict

Python 3.7 throws a deprecation warning for the collections import in renderers.py

[sliverc]

@Yelinz Thanks for reporting. It seems only the Iterable has moved to collections.abc. Such is also referenced in relations.py and views.py.

We could fix this similar as done in DRF where a compat.py is created which does the collections import correctly.

See e.g. https://github.com/encode/django-rest-framework/pull/6473/files

Would you have time to open a PR?

[Yelinz]

When I have some spare time I can do it.