Updated package 2.0.3 added to package manager, which should fix SImpleJson load issue when users upgrade from 2.0.1 to 2.0.3. Added fix to allow unity 2018.2 to default to this new package.

Unable to load "SimpleJson.SimpleJson" from assembly 'UnityEngine.Purchasing' exception occurs when the OnPurchaseSucceeded event is called

Steps to Repro:
1. Open the attached or create a new project
2. Window > Services
3. Enable IAP
4. Import IAP package
5. Open "IAP Demo" scene and play scene
6. Execute any dummy purchase

Actual Result:
1. Observe the error in the console
2. Purchase event fails

Note:
1. IAP Integration guide

https://unity3d.com/learn/tutorials/topics/ads-analytics/integrating-unity-iap-your-game

Occurring with:
2018.3.0a1, 2018.2.0b3, 2018.2.0b1, 2018.2.0a5, 2018.2.0a3

Working with:
2018.1.0f2

Environment:
Windows and Mac

StackTrace:
TypeLoadException: Could not load type 'SimpleJson.SimpleJson' from assembly 'UnityEngine.Purchasing'.
UnityEngine.Purchasing.PurchasingManager.OnPurchaseSucceeded (System.String id, System.String receipt, System.String transactionId) (at /Users/stevenb/unity-src3/Extensions/UnityPurchasing/Runtime/Purchasing/PurchasingManager.cs:111)
UnityEngine.Purchasing.JSONStore.OnPurchaseSucceeded (System.String id, System.String receipt, System.String transactionID)
UnityEngine.Purchasing.FakeStore.<>n__0 (System.String id, System.String receipt, System.String transactionID)
UnityEngine.Purchasing.FakeStore+<>c__DisplayClass15_0.<FakePurchase>b__0 (Boolean allow, PurchaseFailureReason failureReason)
UnityEngine.Purchasing.UIFakeStore+<>c__DisplayClass14_0`1[UnityEngine.Purchasing.PurchaseFailureReason].<StartUI>b__0 (Boolean result, Int32 codeValue)
UnityEngine.Purchasing.UIFakeStore.OkayButtonClicked ()
UnityEngine.Purchasing.UIFakeStore.<InstantiateDialog>b__16_1 ()
UnityEngine.Events.InvokableCall.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:166)
UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:58)
UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:36)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:45)
UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:50)
UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:261)
UnityEngine.EventSystems.EventSystem:Update()