fix(bundle): restore support for JS modules

This change is needed so the bundle can be used with:

```
<script type="module" src="xxxx/socket.io.js"></script>
```

Related:

- https://github.com/socketio/socket.io/discussions/3828
- https://github.com/socketio/socket.io-client/commit/13b32b39a4c1cf4829144fb0a95c4d0506000fb3
- https://github.com/socketio/socket.io-client/commit/8c08c5d5c3bd6dd5477ca11a2625314da57724cc