Oh... Well, that's disappointing. It was a neat tutorial to work through! I'll leave the link up for now just in case the site being down is only temporary, but in the meantime, let me direct you to GameDev.TV's selection of Godot courses. They have some great stuff going on that I'll be jumping back into myself soon. Had to temporarily step away from game dev for health reasons.
https://www.gamedev.tv/products?category_ids%5B%5D=15&page=1