Rust backend still doesn't build

[Brian Leung]

After updating nix/rust-backend/default.nix as well as Cargo.lock, running nix build .#nix.rustBackend fails with

error[E0277]: the trait bound `std::string::String: log::kv::value::ToValue` is not satisfied
  --> /build/rust-backend-0.1.0-vendor.tar.gz/tide/src/log/middleware.rs:43:9
   |
43 | /         log::info!("<-- Request received", {
44 | |             method: method,
45 | |             path: path,
46 | |         });
   | |___________^ the trait `log::kv::value::ToValue` is not implemented for `std::string::String`
   |
   = note: required for the cast to the object type `dyn log::kv::value::ToValue`
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

Here's a branch that has the updates I ran.

[Andika Demas Riyandi]

@leungbk please check with my latest PR.

[Brian Leung]

It works now. Thanks for the quick fix!