SwiftyJSON 4.0 compatibility

[aleciogomes]

With the release of SwiftyJSON 4.0, the init method throws an exception if the data couldn't be parsed into a valid JSON. try can be banged since cache is valid or an empty Dataobject is passed as argument.

[Ruckt]

I went with this:

    private lazy var cachedJSON: JSON = {
        do {
            return try JSON(data: self.data ?? Data())
        }
        catch { return JSON(Data()) }
    }()