can't find crate for `core`

```
error[E0463]: can't find crate for `core`
|
= note: the `wasm32-unknown-unknown` target may not be installed
= help: consider downloading the target with `rustup target add wasm32-unknown-unknown`

error[E0463]: can't find crate for `compiler_builtins`

For more information about this error, try `rustc --explain E0463`.
error: could not compile `cfg-if` due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
cargo build failed
```

I got this error when running `deno task wasmbuild` and the command `rustup target add wasm32-unknown-unknown` didn't work, I am wondering how I should fix this? Thanks!