D7812: examples: specify rustfmt nightly using a $() construct

[gracinet (Georges Racinet)]

gracinet added a comment.


  @pulkit yes, after toolchain reinstall, this rustup which works for me

REPOSITORY
  rHG Mercurial

CHANGES SINCE LAST ACTION
  https://phab.mercurial-scm.org/D7812/new/

REVISION DETAIL
  https://phab.mercurial-scm.org/D7812

To: durin42, #hg-reviewers
Cc: pulkit, quark, gracinet, mercurial-devel