🚀 Updated React CDN to use specific version

Author: ConradSollitt

img/readme/example-code-react.htm

@@ -53,8 +53,8 @@ <h1>Countries</h1>
  );
  </script>
 
- <script src="https://unpkg.com/react@16/umd/react.production.min.js" crossorigin="anonymous"></script>
- <script src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js" crossorigin="anonymous"></script>
+ <script src="https://unpkg.com/react@16.12.0/umd/react.production.min.js" crossorigin="anonymous"></script>
+ <script src="https://unpkg.com/react-dom@16.12.0/umd/react-dom.production.min.js" crossorigin="anonymous"></script>
  <script src="https://cdn.jsdelivr.net/npm/dataformsjs@latest/js/react/es5/DataFormsJS.min.js"></script>
  <script src="https://cdn.jsdelivr.net/npm/dataformsjs@latest/js/react/jsxLoader.min.js"></script>
  </body>