Fixes types in reverse m2m relationships

[Darkheir]

In case of reverse m2m relationships the wrong type was returned.

I created a test to reproduce this situation.

[Darkheir]

fixes #354

[Darkheir]

It seems that my new test triggers an error on Django 1.8 version.

The error is not on the lines added by my commits, but I will try to fix it

[codecov-io]

Codecov Report

Merging #355 into develop will increase coverage by 0.04%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #355      +/-   ##
===========================================
+ Coverage    77.06%   77.11%   +0.04%     
===========================================
  Files           50       50              
  Lines         6027     6038      +11     
===========================================
+ Hits          4645     4656      +11     
  Misses        1382     1382

Impacted Files	Coverage Δ
example/serializers.py	100% <100%> (ø)	⬆️
example/models.py	66.95% <100%> (ø)	⬆️
example/tests/test_utils.py	100% <100%> (ø)	⬆️
rest_framework_json_api/utils.py	90.07% <100%> (+0.28%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ab4e1bd...cce737e. Read the comment docs.

[mblayman]

Hi, @Darkheir. Thanks so much for your contribution! The extra test coverage is really valued. I like the code that I see here. I'd like for all contributors to be recognized for their work so could you add your name to the AUTHORS file? The list of names is alphabetical by first name.

I'm happy to merge after that.

[Darkheir]

Hi, thank you for your kind answer. I just added my name to the contributors.

[mblayman]

Great, thanks again!