Update Attachment.cs

resolves #8

Author: MattReibach

src/SocketLabs/InjectionApi/Message/Attachment.cs

@@ -134,7 +134,7 @@ public Attachment(string name, string mimeType, Stream stream)
         public string ContentId { get; set; }
 
         /// <summary>
-        /// The BASE64 encoded string containing the contents of an attachment.
+        /// The byte array containing the contents of an attachment.
         /// </summary>
         public byte[] Content { get; set; }