Bypass deletion if set to partial update

[thibaut-pro]

Proposal to fix #78

[codecov-commenter]

Codecov Report

Merging #112 into master will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #112      +/-   ##
==========================================
+ Coverage   98.12%   98.13%   +0.01%     
==========================================
  Files           3        3              
  Lines         213      215       +2     
==========================================
+ Hits          209      211       +2     
  Misses          4        4              

Impacted Files	Coverage Δ
drf_writable_nested/mixins.py	98.02% <100.00%> (+0.01%)	:arrow_up:

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[ruscoder]

Hi! Thanks for the contribution. Could you please add tests for your use case?

[MishaGubsky]

Hi! Don't find this impudent but would it be possible to use another serializer parameter (not partial) to make the solution more flexible and save the current logic (the partial parameter already used)?