examples: specify rustfmt nightly using a $() construct
This is ugly, but it's how we have to configure rustfmt for now as we
require nightly rustfmt.
Differential Revision: https://phab.mercurial-scm.org/D7812
hg-core: rustfmt path.rs
The file as vendored does not conform to our source formatting
conventions. Let's reformat it so it does.
# skip-blame automated code reformatting
Differential Revision: https://phab.mercurial-scm.org/D7580