add center in zone serializer

Codecov Report

Merging #351 into master will increase coverage by <.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #351      +/-   ##
==========================================
+ Coverage   81.46%   81.46%   +<.01%     
==========================================
  Files         176      176              
  Lines       11066    11067       +1     
==========================================
+ Hits         9015     9016       +1     
  Misses       2051     2051

Impacted Files	Coverage Δ
arkindex/images/serializers.py	89.83% <100%> (+0.17%)

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merged

mentioned in commit 0d4cd40d