ipynb download button now shows json in browser

[zingale]

In the past few months, when you try to download a notebook using the download button at the top of the page, it displays the notebook as json in the browser instead of downloading it to your local computer. The image below shows the current result from this page (rendered using jupyter-book):
https://zingale.github.io/computational_astrophysics/ODEs/ODEs-implicit.html

This happens for me both when building locally and with the page hosted on github pages