add [Flags] to replication-change-options

StackExchange.Redis/StackExchange/Redis/ReplicationChangeOptions.cs

-namespace StackExchange.Redis
+using System;
+
+namespace StackExchange.Redis
 {
     /// <summary>
     /// Additional operations to perform when making a server a master
     /// </summary>
+    [Flags]
     public enum ReplicationChangeOptions
     {
         /// <summary>