⬆️ Bump graphql from 14.7.0 to 15.5.0

Bumps [graphql](https://github.com/graphql/graphql-js) from 14.7.0 to 15.5.0.
- [Release notes](https://github.com/graphql/graphql-js/releases)
- [Commits](graphql/graphql-js@v14.7.0...v15.5.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -24,7 +24,7 @@
     "unsigned"
   ],
   "peerDependencies": {
-    "graphql": "^14.0.2"
+    "graphql": "^15.5.0"
   },
   "devDependencies": {
     "babel-cli": "^6.26.0",
@@ -37,7 +37,7 @@
     "eslint-plugin-node": "^8.0.0",
     "eslint-plugin-promise": "^4.0.1",
     "eslint-plugin-standard": "^4.0.0",
-    "graphql": "^14.0.2",
+    "graphql": "^15.5.0",
     "graphql-tools": "^4.0.3",
     "mocha": "^5.2.0",
     "nyc": "^13.1.0"