The `cbor` crate has been unmaintained for several years, and depends on
the ancient `rustc_serialize` crate which (a) doesn't build on WASM, and
(b) doesn't build when we use a minimal-dep Cargo.lock. (The latter is
because cbor specifies rustc_serialize 0.3.0 when it should specify 0.3.1,
but there is nothing we can do to fix that when cbor is unmaintained.)
This changes a hardcoded value in a regression test, but it's because
we're replacing the serialization engine rather than changing our code,
so this is not actually a change.
b03602bfaa