继承自 NSManagedObject 的对象无法解析

```swift
@objc(OAuthModel)
final class OAuthModel: NSManagedObject, HandyJSON {
@NSManaged public var access_token: String?
}

let dic: [String : Any] = [
"access_token" : "78491447f77ca068a6211b7bf5aff725",
]

let model = try? OAuthModel.deserialize(from: dic)
print(model!.access_token ?? "null")
```

如上代码，继承自 NSManagedObject 的对象，解析后，属性为 nil

Start by reproducing the issue with the OAuthModel and dictionary shown in the report, then trace HandyJSON's deserialization path for NSManagedObject subclasses. Done means the deserialized OAuthModel has the supplied access_token value instead of nil, with regression coverage for this case.

Written by the indexing model from the issue text.