Fix: "Firebase hosting setup complete" alert/error when deploying Angular 6 app to firebase hosting
How to install Boostrap 4-beta.2 in Angular 4+ as a dependency.
This has been updated to use Bootstrap Beta.2 (Latest stable) as of April. 12, 2018.
This also works with Angular 5, But not Angular 6. For Angular 6 you can use this post.
I'm aware that BS4 (non-beta) has been released, however there is a bug with ng5 cli and Bootstrap 4, so sticking with Beta.2 is your best bet for now. I'll update when the bug is fixed.