ExpressJS graceful shutdown example.

• install dependencies npm i
• start the application node index.js
• connect to the server telnet 127.0.0.1 3000
• stop the application with ctrl-c
• application will not stop because of the active client connection
• type GET / HTTP/1.1 on terminal with the telnet session and press enter/return twice
• you will see the server response with Connection: Close response header and connection will be terminated, then application will exit
• comment out the line containing res.set('Connection', 'Close');
• start the application and repeat all the steps
• connection will not be terminated and application will not exit until killed or connection closed by the client