Use lastest 1.xx Rust version in Docker build

Use lastest 1.xx Rust version in Docker build

With the previous Rust version 1.61, the build fails with

> error[E0658]: use of unstable library feature 'scoped_threads'

This has been "stabilized" in Rust 1.63. To avoid the hassle
of manually updating the version, we can just default to the
latest minor release.