Fix file+json data post

[GuillaumeCisco]

When posting to a django rest framework model with a file attribute, data is json stringified, so we need to json load it in order to get it.

[codecov]

Codecov Report

Merging #20 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   81.39%   81.48%   +0.08%     
==========================================
  Files           4        4              
  Lines         129      135       +6     
==========================================
+ Hits          105      110       +5     
- Misses         24       25       +1

Impacted Files	Coverage Δ
parler_rest/fields.py	73.4% <100%> (+0.67%)	⬆️

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[codecov]

Codecov Report

Merging #20 into master will increase coverage by 0.22%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   81.39%   81.61%   +0.22%     
==========================================
  Files           4        4              
  Lines         129      136       +7     
==========================================
+ Hits          105      111       +6     
- Misses         24       25       +1

Impacted Files	Coverage Δ
parler_rest/fields.py	73.68% <100%> (+0.95%)	⬆️

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[vdboor]

Hi!

Thanks for this pull request! Aside from a small change, this looks ok to merge.
Do you have a bit of test code that shows when this situation occurs? A unit test would even be better!

[GuillaumeCisco]

Ok @vdboor, just added a little test. As said above it simulates the translations field is sent as a json dumps. Useful when uploading file and data.
Cheers.