Avoid exception in AutoPrefetchMixin when including a reverse one to one relation

[santiavenda2]

Fixes #537

Description of the Change

Fix AutoPrefetchMixin when include have a one to one relation

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• changelog entry added to CHANGELOG.md
• author name in AUTHORS

[codecov]

Codecov Report

Merging #536 into master will increase coverage by 0.01%.
The diff coverage is 96.15%.

@@            Coverage Diff             @@
##           master     #536      +/-   ##
==========================================
+ Coverage   94.33%   94.34%   +0.01%     
==========================================
  Files          60       61       +1     
  Lines        3725     3750      +25     
==========================================
+ Hits         3514     3538      +24     
- Misses        211      212       +1

Impacted Files	Coverage Δ
example/tests/integration/test_includes.py	100% <100%> (ø)	⬆️
rest_framework_json_api/views.py	94.34% <100%> (+0.04%)	⬆️
example/serializers.py	100% <100%> (ø)	⬆️
example/migrations/0006_auto_20181228_0752.py	100% <100%> (ø)
example/models.py	90.65% <87.5%> (-0.26%)	⬇️

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[codecov]

Codecov Report

Merging #536 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #536      +/-   ##
==========================================
+ Coverage   95.47%   95.51%   +0.04%     
==========================================
  Files          54       55       +1     
  Lines        2804     2829      +25     
==========================================
+ Hits         2677     2702      +25     
  Misses        127      127

Impacted Files	Coverage Δ
example/tests/test_views.py	100% <ø> (ø)	⬆️
example/tests/conftest.py	100% <100%> (ø)	⬆️
example/models.py	100% <100%> (ø)	⬆️
example/tests/integration/test_includes.py	100% <100%> (ø)	⬆️
example/factories.py	98.76% <100%> (+0.09%)	⬆️
example/migrations/0006_auto_20181228_0752.py	100% <100%> (ø)

---

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[sliverc]

Thanks for working on this. Fix looks good to me, there is just one question concerning test.

[sliverc]

when authors.bio.metadata is requested to be included shouldn't there be a authorsBioMetadata type be included as well?

[santiavenda2]

Added AuthorBiosMetadata on Serializarers. I change the tests to reflect that.

[sliverc]

@santiavenda2
Merged. Thanks for your contribution.