555: Update to latest web-sys r=kvark a=grovesNL
Cherry-pick #497 into `master` now that new versions of web-sys/wasm-bindgen/js-sys/wasm-bindgen-futures are published.
We could also do this for `v0.6` too if we want CI to succeed there, or alternatively consider disabling CI for wasm builds on `v0.6`.
Co-authored-by: Joshua Groves <josh@joshgroves.com>