Adding explicit json_serialize argument in AIOHTTPTransport

[leszekhanusz]

Fix issue #332

[codecov-commenter]

Codecov Report

Merging #337 (ecf6915) into master (3970f1c) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #337   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           26        26           
  Lines         2231      2232    +1     
=========================================
+ Hits          2231      2232    +1     

Impacted Files	Coverage Δ
gql/transport/aiohttp.py	100.00% <100.00%> (ø)

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