D8448: rust-chg: modernize entry function

[durin42 (Augie Fackler)]

durin42 added inline comments.

INLINE COMMENTS

> main.rs:70
> +#[tokio::main]
> +async fn run(umask: u32) -> io::Result<i32> {
>      let mut loc = Locator::prepare_from_env()?;

With this series I get lots of

`+  error[E0670]: `async fn` is not permitted in the 2015 edition`

from `test-check-rust-format.t`. Am I doing something wrong?

REPOSITORY
  rHG Mercurial

CHANGES SINCE LAST ACTION
  https://phab.mercurial-scm.org/D8448/new/

REVISION DETAIL
  https://phab.mercurial-scm.org/D8448

To: yuja, #hg-reviewers
Cc: durin42, mercurial-devel