Update serializer.rst
minor #965 Update serializer.rst (ruslan-polutsygan)

This PR was submitted for the master branch but it was merged into the 1.2 branch instead (closes #965).

Discussion
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Update serializer.rst

Before - http://i.imgur.com/hTYzHGR.png
After - http://i.imgur.com/SAPhNN7.png

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a8ab1f8 Update serializer.rst