Bump @types/react from 16.8.23 to 16.9.4 in /app (#215)

Bumps [@types/react](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/react) from 16.8.23 to 16.9.4.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/react)

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

app/package.json

@@ -59,7 +59,7 @@
     "@types/get-value": "^3.0.1",
     "@types/node": "^12.7.8",
     "@types/prismjs": "^1.9.1",
-    "@types/react": "^16.8.23",
+    "@types/react": "^16.9.4",
     "@types/react-dom": "^16.0.11",
     "@types/react-redux": "^7.0.9",
     "@types/react-resize-detector": "^4.0.1",