Juraj:
package installs in IDE 1.8.8 on Linux
Thank you for the info. I am using 1.8.9 on Windows. I have other board definitions on File/Preferences/Additional Boards Manager URL's and they work fine, it seems like there is something wrong with the URL but as I mentioned, I can access the .json file from my browser when I paste the same URL to the address box.
Does anyone know how to make this boards definitions permanent in The IDE rather than constantly loading the .json file from the internet?