example_yaml: netcat client closes connection after EOF

From the nc(1) man page:

     -N shutdown(2) the network socket after EOF on the input. Some servers
        require this to finish their work.

Ubuntu would appear to be one such server.

guide/blueprints/example_yaml/vanilla-bash-netcat-w-client.yaml

@@ -66,7 +66,7 @@ services:
       name: sayHiNetcat
       description: Echo a small hello string to the netcat entity
       command: |
-        echo $message | nc $TARGET_HOSTNAME 4321
+        echo $message | nc -N $TARGET_HOSTNAME 4321
       parameters:
         message:
           description: The string to pass to netcat