`use proc_macro::...` -> `use crate::proc_macro::...` in examples?

[anp]

In a 2018 edition crate, the recent module system changes prevent the current README example from working on a recent nightly. Referencing the proc_macro crate as crate::proc_macro appears to resolve the problem for me. Is this the correct fix?

[dtolnay]

Yes, I would use crate::proc_macro:: until we land the stabilization (and possibly backport) for rust-lang/rust#55599. Let's update the documentation to use 2018 edition as soon as the edition is officially released.

[dtolnay]

Updated example code to 2018 edition in 87f7291.