point to api 2.1 for binary send example

Author: AaronWDS

launcher-csharp/eSignature/Examples/CreateEnvelopeWithMultipleDocumentTypes.cs

@@ -61,7 +61,7 @@ public static (bool statusOk, string envelopeId, string errorCode, string errorM
             byte[] hyphens = Encoding.ASCII.GetBytes("--");
 
             string uri = basePath
-                    + "/v2/accounts/" + accountId + "/envelopes";
+                    + "/v2.1/accounts/" + accountId + "/envelopes";
             HttpWebRequest request = WebRequest.CreateHttp(uri);
 
             request.Method = "POST";