Previous link of Code Splitting on course website redirect to itself

On the course website, [Code Splitting](https://btholt.github.io/complete-intro-to-react-v5/code-splitting)'s previous link just redirects to itself.
As far as I can tell, in the gh-pages-src branch, [lessons/code splitting.md](https://github.com/btholt/complete-intro-to-react-v5/blob/gh-pages-src/lessons/code-splitting.md)'s `order` in metadata should be `18` instead of `19`. Currently both [code splitting.md](https://github.com/btholt/complete-intro-to-react-v5/blob/gh-pages-src/lessons/code-splitting.md) and [typescript.md](https://github.com/btholt/complete-intro-to-react-v5/blob/gh-pages-src/lessons/typescript.md) share the same order `19`.

Open gh-pages-src/lessons/code-splitting.md and compare its metadata with lessons/typescript.md, focusing on the shared order value. Correct the ordering metadata so the course navigation no longer points Code Splitting to itself, then verify the rendered course page's previous link.

Written by the indexing model from the issue text.