Pin react-lifecycle-visualizer version for demo

This prevents failure of the StackBlitz demo if there's problem with a newly released minor or patch version.

Author: Oblosys

examples/parent-child-demo/package.json

@@ -15,6 +15,6 @@
     "react": "^17.0.1",
     "react-dom": "^17.0.1",
     "react-hot-loader": "^4.13.0",
-    "react-lifecycle-visualizer": "^2.2.11"
+    "react-lifecycle-visualizer": "2.2.11"
   }
 }