Message class implements Dispose method

The Message class implements the Dispose method. 
The Message class must follow the dispose pattern to ensure it's disposed in all paths.
with 'using()' we can enforce the dispose pattern.

Author: sandervandevelde

articles/iot-edge/tutorial-csharp-module.md

@@ -207,14 +207,16 @@ Currently, Visual Studio Code can develop C# modules for Linux AMD64 and Linux A
             {
                 Console.WriteLine($"Machine temperature {messageBody.machine.temperature} " +
                     $"exceeds threshold {temperatureThreshold}");
-                var filteredMessage = new Message(messageBytes);
-                foreach (KeyValuePair<string, string> prop in message.Properties)
+                using (var filteredMessage = new Message(messageBytes))
                 {
-                    filteredMessage.Properties.Add(prop.Key, prop.Value);
-                }
+                    foreach (KeyValuePair<string, string> prop in message.Properties)
+                    {
+                        filteredMessage.Properties.Add(prop.Key, prop.Value);
+                    }
 
-                filteredMessage.Properties.Add("MessageType", "Alert");
-                await moduleClient.SendEventAsync("output1", filteredMessage);
+                    filteredMessage.Properties.Add("MessageType", "Alert");
+                    await moduleClient.SendEventAsync("output1", filteredMessage);
+                }
             }
 
             // Indicate that the message treatment is completed.