fix(playground): graphql-tools version downgrade

[vasilev-alex]

Issue Reference this PR resolves

#661

Description of Changes Made (if issue reference is not provided)

Downgraded graphql-tools version

[codecov-commenter]

Codecov Report

Merging #665 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #665   +/-   ##
=======================================
  Coverage   80.69%   80.69%           
=======================================
  Files          40       40           
  Lines        3316     3316           
=======================================
  Hits         2676     2676           
  Misses        640      640           

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