Fix unicode as object type

[lmazuel]

Fix #221

[codecov-commenter]

Codecov Report

Merging #222 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #222      +/-   ##
==========================================
+ Coverage   86.22%   86.23%   +0.01%     
==========================================
  Files          25       25              
  Lines        2736     2738       +2     
==========================================
+ Hits         2359     2361       +2     
  Misses        377      377              

Impacted Files	Coverage Δ
msrest/serialization.py	91.11% <100.00%> (+0.01%)	⬆️

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