[Doc missing] src/store/StoreMixin.js

In the official favourite location source,

```
class LocationStore {
constructor() {
this.locations = [];
this.errorMessage = null;

this.bindListeners({
handleUpdateLocations: LocationActions.UPDATE_LOCATIONS,
handleFetchLocations: LocationActions.FETCH_LOCATIONS,
handleLocationsFailed: LocationActions.LOCATIONS_FAILED,
setFavorites: LocationActions.FAVORITE_LOCATION
});

this.exportPublicMethods({
getLocation: this.getLocation
});

this.exportAsync(LocationSource);
}
//...
}
```

"exportAsync" cannot be found anywhere in the documentation.