The 1.31.1 pre-release is ready for testing. It’s scheduled to be released on Thursday 20th. Release notes can be found here: https://github.com/rust-lang/rust/blob/stable/RELEASES.md .
You can try it out locally with:
RUSTUP_DIST_SERVER=https://dev-static.rust-lang.org rustup update stable
The index is https://dev-static.rust-lang.org/dist/2018-12-19/index.html.