Array ```items``` keyword limited to single item

Given a schema:

```
{
  properties: {
    signatures: {
      type: 'array',
      items: { type: 'object' }
    }
  }
}
```

and input: ```{ signatures: [ { foo: 'bar' }, { baz: 'qux' } ] }```

results in: ``` { signatures: [ { foo: 'bar' } ] }```