Resource system does not allow keys like "h1"

### Problem description

Using a key in a json resource file like "h1" does not work. The schema check states property "h1" is not allowed.

### Expected behavior

Any reasonable valid string should be allowed.

### Environment

- Tabris.js version: 3.7

### Code snippet

```js
{
"$schema": "../../node_modules/tabris/schema/fonts.json",
"h1": {
"size": 96
}
}
```