Bump graphql to 1.9.12
This MR bumps graphql to 1.9.12 to keep the Debian version in sync.
Gem changelog for 1.9.12: https://github.com/rmosolgo/graphql-ruby/blob/master/CHANGELOG.md#1912-9-sept-2019
CC: @rpaik - hackathon MR :)
Edited by charlie ablett