Added missing end_of_stream attribute from ticket export (#518)

Author: JeremyCrookshank

src/ZendeskApi_v2/Models/Tickets/GroupTicketExportResponse.cs

@@ -31,6 +31,9 @@ public class GroupTicketExportResponse
         [JsonProperty("next_page")]
         public string NextPage { get; set; }
 
+        [JsonProperty("end_of_stream")]
+        public bool EndOfStream { get; set; }
+
         [JsonProperty("organizations")]
         public IList<Organization> Organizations { get; set; }