`LineItem` won't serialize as a parameter

[nwithan8]

easypost-csharp/EasyPost/Parameters/Shipment/Create.cs

Line 167 in 1983fe7

public class LineItem

The LineItem class is missing an inheritance from BaseParameters and JsonProperty attributes that would allow it to be serialized in a parameter payload.

See the relationship between CustomsInfo.Create.CustomsItems and Models.API.CustomsItem for reference.