createOrders OrdRefId

[LadisCZ]

Hi,

https://github.com/Salamek/PplMyApi/blob/master/src/Api.php#L292

The column name for Order Reference ID is "OrdRefId", not "OrdRefID" (https://myapi.ppl.cz/MyAPI.svc?singleWsdl).

The current field name results in a response "OrdRefId is a mandatory field".

[Salamek]

@LadisCZ fixed