support Django 2 + in tests

[urbandove]

Foreign keys in Django 2 require an on_delete attribute
Also the field.rel attribute has been deprecated as of Django 2 and is now field.remote_field
I have added a fallback for 1.8

The django docs specifying the changes to field.rel

[coveralls]

Coverage decreased (-0.6%) to 92.528% when pulling d314d10 on urbandove:django2 into 24706f5 on graphql-python:master.

[coveralls]

Coverage decreased (-0.8%) to 92.347% when pulling 384bff0 on urbandove:django2 into 24706f5 on graphql-python:master.

[coveralls]

Coverage decreased (-0.8%) to 92.347% when pulling 384bff0 on urbandove:django2 into 24706f5 on graphql-python:master.

[coveralls]

Coverage decreased (-0.8%) to 92.347% when pulling 384bff0 on urbandove:django2 into 24706f5 on graphql-python:master.

[urbandove]

I should note that in my previous pull request #335 i added on_delete attribute to all related fields - as this is a required field starting in 2.0 (but supported before)

[coveralls]

Coverage increased (+0.02%) to 93.163% when pulling 489d287 on urbandove:django2 into 24706f5 on graphql-python:master.

[urbandove]

Have updated python version in setup.py so that if its python 2 it doesnt try install django 2
this makes build pass - which hasnt been happening till now

[coveralls]

Coverage increased (+0.02%) to 93.163% when pulling f687406 on urbandove:django2 into 24706f5 on graphql-python:master.

[coveralls]

Coverage increased (+0.02%) to 94.799% when pulling 43c0c99 on urbandove:django2 into a480a39 on graphql-python:master.

[urbandove]

Now the 2.0 tests are failing because pytest-django has not released a version which supports 2.0 (Coming in version 3.1.3)
(Also -the current pytest-django version is pinned at an old version anyways)
We can wait for the new version to be push or pip install directly from the github master branch

[spockNinja]

Thanks for your work here! It's looking great so far.

It looks like pytest-django 3.1.3 is coming pretty soon, so my vote would be to wait for that and then we can update the test_requires to unpin/update it.

If you want to try out their master in the meantime to make sure it doesn't break anything else, that might be a good next move. There's always a chance that updating to their master will cause older python/django versions to break.

[spockNinja]

For now, I'm going to steal this bit so we can at least get new PRs passing their builds.

django_version = 'Django>=1.8.0,<2' if sys.version_info[0] < 3 else 'Django>=1.8.0'

[spockNinja]

I cherry-picked your 489d287 commit into #338 so we can get other builds passing again.

[urbandove]

Hi @spockNinja
pytest-django finally updated their pypi version to 3.2.1 which supports django2. So now this patch is ready to go.
There is the field.remote field change from an if-else to a try-catch - which I think is the accepted way for dealing with deprecated fields.