Fix `value` property of `RadioButtonInput`s

Example code:

```javascript
Section (
    Label (
        RadioButtonInput({group: "radioButtons", value: true}) (),
        "Radio button 1"
    ),
    Label (
        RadioButtonInput({group: "radioButtons"}) (),
        "Radio button 2"
    )
)
```

When rendered, the second radio button is selected by default instead of the first one.