dependency: bump graphql from 15.5.3 to 15.6.0

Bumps graphql from 15.5.3 to 15.6.0.

Release notes

Sourced from graphql's releases.

v15.6.0 (2021-09-20)

New Feature 🚀

• #3267 Depreacate 'VisitorKeyMap' and backported 'ASTVisitorKeyMap' type (@​IvanGoncharov)

Committers: 1

• Ivan Goncharov(@​IvanGoncharov)

Commits

• 1532910 15.6.0
• 201ed90 Depreacate 'VisitorKeyMap' and backported 'ASTVisitorKeyMap' type (#3267)
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