Update examples to codepin on documentation webpage (https://reactcommunity.org/react-modal/)

[andrewright]

Summary:

Steps to reproduce:

1. Open https://reactcommunity.org/react-modal/examples/minimal/
2. Click: Minimal example
3. Check JS version in JS sources

Expected behavior:

Used library version: 1.6.2 Current version: 3.14.3

Additional notes:

Problem is not just by this link. Here: https://www.npmjs.com/package/react-modal in the end of the page, in example heading - also link to codepin with old version of react-modal