Rust nightly + formatting changes
One of the challenges of using Rust nightly is that things can change
often. Master builds have been failing because CI is picking up the latest
nightly all the time, and the formatting rules change over time.
One option to avoid this is to have CI use a specific nightly version
rather than always using the latest, and then we can use PRs to update the
nightly version being used. For example we can have the CI script run the
rustup default nightly-2018-12-05
If there are no objections I will create a JIRA issue for this.