ignore `@substrate/connect` source map WARNING

### solution

disable sourcemap

```json
"start": "GENERATE_SOURCEMAP=false react-scripts start",
```

or set it to `.env`

see https://create-react-app.dev/docs/advanced-configuration/

### reason

`@substrate/connect` **may** did not provide `.map` files for webpack sourcemap analyzer.

### dependency relationship

`"@polkadot#api#@polkadot#rpc-provider#@substrate#connect"`