Investigate and fix build error in wasm-test-runner

[th4s]

Currently our wasm-test-runner fails with

error[E0599]: no method named `clone` found for struct `JsStatic` in the current scope
  --> /home/th4s/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wasm-bindgen-rayon-1.2.1/src/lib.rs:81:13
   |
81 |         URL.clone()
   |             ^^^^^ method not found in `JsStatic<JsString>`

For more information about this error, try `rustc --explain E0599`.
error: could not compile `wasm-bindgen-rayon` (lib) due to 1 previous error

To reproduce go into wasm-test-runner and do a cargo clean && cargo update then execute ./run.sh.

[th4s]

Probably related to a recent update of js-sys but I could not get it working spending a few minutes on downgrading js-sys. Probably more crates need to be down-graded.

[th4s]

Eventually related: rustwasm/wasm-bindgen#4057

[th4s]

This can be more easily reproduced by cd into crates/wasm and then doing a cargo check -F no-bundler. It seems that this feature is causing it.

[th4s]

Closed by #567