Hi! I think you want to update the swift-tools dependency at the top of Package.swift in KituraWebInterface_Starter. You have it at 4.1, which I believe is the version that ships with Xcode 9.3, which is High Sierra-only. I got it to build (on 10.12.6, Xcode 9.2) by changing that to 4.0.
A very great tutorial. I was modifying it for my project where I tried to pass unicode characters like in the text field, the characters doesnโt render correctly in the frontend. I checked the database from terminal where it shows that it has been saved correctly. Any suggestions how to render the unicode characters?