Jupyter-book: Update documentation links that are broken

[choldgraf]

In https://github.com/jupyter/jupyter-book/commit/12dd61e01eeff4d7a4ee14a9b862b8aea6c92cce @habi noticed that some links that we thought were fixed are actually still broken, we should fix them!

@habi if you wanted to give it a shot (the fix would be here: https://github.com/jupyter/jupyter-book/tree/master/jupyter_book/book_template instead of in the /minimal directory) I'm happy to review a PR! :-)

[habi]

I'll see what I can do, but not before next week...

[choldgraf]

Is this one resolved for you now @habi?

[habi]

The link on https://jupyter.org/jupyter-book/features/notebooks.html is now correct, yes.

[choldgraf]

Thanks so much for making the fix!