changed else if check to correct image GUID for image tracking demo, reported via https://github.com/Unity-Technologies/arfoundation-demos/issues/51

Assets/ImageTracking/Scripts/ImageTrackingObjectManager.cs

             {
                 Destroy(m_SpawnedOnePrefab);
             }
-            else if (image.referenceImage.guid == s_FirstImageGUID)
+            else if (image.referenceImage.guid == s_SecondImageGUID)
             {
                 Destroy(m_SpawnedTwoPrefab);
             }