Drop support for Django 1.8 - 1.10

[mblayman]

The effect of dropping support for Django 1.8 - 1.10 is pretty huge. Lots of test environments can go away.

Python 3.3 is EOL so I dropped that.

Django 1.8 - 1.10 are (basically) EOL so I dropped them.

Django REST Framework doesn't support Django 1.11 until a bug fix release of DRF 3.6.x so I dropped those too.

If the tests go green, I'll begin removing the old bits that are in the package files.

Fixes #386

[codecov-io]

Codecov Report

Merging #387 into master will decrease coverage by 0.19%.
The diff coverage is 93.33%.

@@            Coverage Diff            @@
##           master     #387     +/-   ##
=========================================
- Coverage   92.57%   92.37%   -0.2%     
=========================================
  Files          56       56             
  Lines        2921     2887     -34     
=========================================
- Hits         2704     2667     -37     
- Misses        217      220      +3

Impacted Files	Coverage Δ
setup.py	80% <ø> (ø)	⬆️
rest_framework_json_api/views.py	95.06% <100%> (-0.8%)	⬇️
rest_framework_json_api/relations.py	82.75% <100%> (-0.1%)	⬇️
rest_framework_json_api/__init__.py	100% <100%> (ø)	⬆️
rest_framework_json_api/utils.py	91.13% <87.5%> (+0.33%)	⬆️
rest_framework_json_api/metadata.py	25% <0%> (-3.34%)	⬇️
example/api/serializers/__init__.py	75% <0%> (-3.19%)	⬇️

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[mblayman]

I'll leave this open for comment for a week or two. If people are cool with it, we can merge it and move into the future! 😄

[sliverc]

Great... I like it when this gets cleaned up.
Technically Django 1.8 is still supported till April next year - I do not mind to drop it others might comment on that though (they could still use old versions though)

There are several spots in the code where django.VERSION is checked... I think some of those checks could be removed now.

[mblayman]

Right about Django 1.8. I figured DJA 2.3.1 can be the end of the line for 1.8.

This PR clears out all the django.VERSION checks. 😄

[sliverc]

Nice 👍

It might be good to reference the issue why only version DRF 3.6.3 supports Django 1.11. I haven't found it with a quick search.

[mblayman]

That would be nice. I didn't base that off an issue because I couldn't find one. I went source diving and looked at the DRF tags on GitHub and browsed through the tags until I found the first one that mentions 1.11 on the README. 3.6.3 was it.

[sliverc]

The PRs seem to be:

encode/django-rest-framework#5081
encode/django-rest-framework#5062

which were only released with 3.6.3. So this looks good.

[mblayman]

Awesome. I appreciate you checking on that. It's nice to have confirmation of when the support for 1.11 was added.

[amw]

I fully approve and eagerly await release. For some reason an older release of DRF JSON API that I have been using works for me after upgrading to Django 2.0, but I feel uncomfortable about it.

[mblayman]

I open this 10 day ago and have only seen positive feedback so I'm going to go ahead and merge it.