dot.dot Nothing happens

I'm trying to convert an object to dot notation with dot.dot by running

```js
const target = dot.dot({
  a: 1,
  b: 2,
  c: {
    d: 3,
    e: {
      f: 4,
    },
  },
})
```

Expected result
```js
{
  a: 1,
  b: 2,
  'c.d': 3,
  'c.e.f': 4,
}
```

But when i'm logging `target` it always result in the default object, nothing happens.

I'm using version 2.1.4.