Fix variable_values spelling in docs

[wilbertom]

No description provided.

[codecov-commenter]

Codecov Report

Merging #226 (4400d46) into master (c98d8e2) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #226   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           16        16           
  Lines         1064      1064           
=========================================
  Hits          1064      1064           

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

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[leszekhanusz]

Thanks