minor change to prompt

threaded-server.py

@@ -33,7 +33,7 @@ sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 # process command line arguments
 argc = len(sys.argv)
 if argc != 2:
-    print ("usage: python3 server.py serverPort")
+    print ("usage: python3 threaded-server.py serverPort")
     sys.exit()
 port = int(sys.argv[1])