Add Version property to HistoryEvent class

Author: AnatoliB

src/DurableSDK/HistoryEvent.cs

@@ -50,6 +50,9 @@ internal class HistoryEvent
 
         [DataMember]
         public string Name { get; set; }
+
+        [DataMember]
+        public string Version { get; set; }
 
         [DataMember]
         public string Result { get; set; }