Keep shipment index non-optional

Author: itsmeichigo

Modules/Sources/Storage/Model/WooShippingShipment+CoreDataProperties.swift

@@ -8,7 +8,7 @@ extension WooShippingShipment {
 
     @NSManaged public var siteID: Int64
     @NSManaged public var orderID: Int64
-    @NSManaged public var index: String?
+    @NSManaged public var index: String
     @NSManaged public var shippingLabel: ShippingLabel?
     @NSManaged public var items: Set<WooShippingShipmentItem>?
     @NSManaged public var order: Order?

Modules/Sources/Yosemite/Model/Storage/WooShippingShipment+ReadOnlyConvertible.swift

@@ -20,7 +20,7 @@ extension Storage.WooShippingShipment: ReadOnlyConvertible {
 
         return WooShippingShipment(siteID: siteID,
                                    orderID: orderID,
-                                   index: index ?? "0",
+                                   index: index,
                                    items: shipmentItems,
                                    shippingLabel: shipmentShippingLabel)
     }