Fix custom array schema

[cnizzardini]

Fixes custom array schema's resulting in output like this in swagger:

{
  "array_property": [
    "string"
  ]
}

Now supports defining custom array like this:

(new SchemaProperty('foo_schemas', 'array'))->setItems([
    [
        'type' => 'object',
        'allOf' => [['$ref' => '#/components/schemas/FooSchema']]
    ]
]),

outputting...

"foo_schemas": [
  {
    "id": 0,
    "name": "string",
  }
],