No Exception raised?

Hello!

I have a following sample schema:

```json
"schema": {
  "type": "object",
    "properties": {
      "value": {"type": "integer"}
    }
}
```

and

```python
validate({"non_existent_property": "test"}, schema)
```

does not raise an Exception.

Is it ok?
I've thought it should. 