Error when using Jsona on Nuxt server side

When importing Jsona as suggested in the readme:

```ts
import Jsona from 'jsona'
```

It is resulting in a `Jsona is not a constructor` error when using by a [Nuxt](https://nuxt.com/) application on the server-side.

I have found that using the named import works

```ts
import { Jsona } from 'jsona'
```

Jsona version `1.12.1`