Wrong attribute name HorizontalApi

[TigerTom]

Hi,

I believe in the Class Dpi, which is in namespace GoogleCloudPrintApi.Models.Printer.
There is a typo in the class OptionType.

Where it should be "HorizontalDpi" instead of "HorizontalApi" and "VerticalDpi" instead of "VerticalApi".
The json that is then outputted is being rejected from Google.

Thanks.