Update Rust version

Some of the new features are needed for future FIDL support.

ref project-oak#426

Dockerfile

@@ -60,7 +60,9 @@ RUN chmod a+rwx ${RUSTUP_DIR}
 
 # Install Rust toolchain.
 # We currently need the nightly version in order to be able to compile some of the examples.
-ARG RUST_VERSION=nightly-2019-07-18
+# See https://rust-lang.github.io/rustup-components-history/ for how to pick a version that supports
+# the appropriate set of components.
+ARG RUST_VERSION=nightly-2020-01-08
 RUN rustup toolchain install ${RUST_VERSION}
 RUN rustup default ${RUST_VERSION}