Rust: rust tutorial can not be compiled with rust edition 2018

The rust compiler is broken for rust edition 2018. If we change the tutorial cargo (tutorial/rs/Cargo.toml) to edition = "2018", the following error would occur:

// code placeholder
error[E0432]: unresolved import `shared`
  --> src/tutorial.rs:30:5
   |
30 | use shared;
   |     ^^^^^^ no `shared` external crateerror: aborting due to previous error

 The compiler might need to generate use crate::shared instead.