Add ArrayTypeGenerator

[jordanaubert]

When i get the array property foo :

"foo": {
    "10": 3.333,
    "11": 5.555
}

The JSON does not validate :

 JSON does not validate. Violations:
        - [foo] Object value found, but an array or a null is required
       (Exception)

according to the item schema :

"foo": {
    "type": [
         "array",
         "null"
    ]
}

Adding the type object in the schema should fix the problem.