Tell Rust it's the nightly channel.

BUG=b:193076633
TEST=CQ+1

Change-Id: I4787667cced1e705c9fdb6ff550db339b3c19488
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/3213392
Tested-by: Bob Haarman <inglorion@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
6 files changed