projection $slice error

**Enviroment**
PHP: 7.0.11
Library: 1.0.3
Mongodb: 3.2.9
Extension: mongodb-1.2.0alpha3

When i make a query using the mongo-php-library as this

``` php
$collection->find([], 
    [
        'projection' => [ 'users' => ['$slice' => 10] ]
    ]
);
```

I got an error:
**Cannot use $-modifiers or empty keys in 'opts'.**

Can anyone help me?
Is the '$slice' deperated?
