Update Cargo.lock files

Recent versions of the Rust compile tool `cargo` insert a comment at the
top of `Cargo.lock` indicating that this file is auto-generated.  Commit
versions of these files with this comment in, so that users of recent
versions of Rust will not have sprious diffs everytime they compile.

Older versions of Rust will remove these lines.  However, this is less
likely to be an issue, as we now depend on at least Rust 1.31 in order
to have Rust 2018 support.  We recommend using 'rustup' to keep the Rust
install up to date.

Signed-off-by: David Brown <david.brown@linaro.org>

Author: d3zd3z