Add graphql@~15.0 to CI matrix

Author: robhogan

.circleci/config.yml

@@ -12,7 +12,7 @@ workflows:
           # definitions for field extensions in older @types/graphql versions
           matrix:
             parameters:
-              graphql-version: ["~0.13", "~14.0", "~14.5", "~14.6"]
+              graphql-version: ["~0.13", "~14.0", "~14.5", "~14.6", "~15.0"]
       - test-and-build:
           # Leave graphql-version unspecified to respect the lockfile and also run tsc
           name: test-and-build-with-typecheck