reference type google.maps directive missing from 1.6.10

Hey there,

Up until v1.6.8 of this package the following line was included in `dist/index.d.ts`:

```js
///
```

Since updating to v1.6.10 I noticed this line has been removed. This is causing breakage across our CI/CD workflows with code like this:

```
// my-map.ts
let map: google.maps.Map;
```

Now erroring with:

```
"error TS2503: Cannot find namespace 'google'."
```

Looking through the changelog I can't really see why the line was removed. Was this intentional or an unintentional side effect of a dependency update?

Adding the removed type reference to my-map.ts resolves the issue but it'd be good to know if this is planned to be added back in before I have to go update a load of different projects 😅