Live update preview doesn't work for rust projects

[gabbifish]

🐛 Bug Report

Environment

• operating system:
• output of rustc -V: rustc 1.36.0 (a53f9df32 2019-07-03)
• output of node -v: v8.10.0
• output of wrangler -V: wrangler 1.2.0

Steps to reproduce

wrangler generate rust-test --type=rust
cd rust-test
wrangler preview --watch

What did you expect to see?

Live reload should successfully stay alive

What did you see instead?

$ wrangler preview --watch
⬇️ Installing wasm-pack...
 Compiling your project to WebAssembly...
[INFO]: Checking for the Wasm target...
[INFO]: Compiling to Wasm...
    Finished release [optimized] target(s) in 0.01s
[INFO]: Installing wasm-bindgen...
[INFO]: Optional fields missing from Cargo.toml: 'description', 'repository', and 'license'. These are not necessary, but recommended
[INFO]: :-) Done in 0.09s
[INFO]: :-) Your wasm pkg is ready to publish at ./pkg.
⬇️ Installing wasm-pack...
Error: Your JavaScript project is missing a `package.json` file; is `./` the wrong directory?