Increase resilience and simplify the implementation

I have a suggestion to improve the resilience and align a bit more with industry standards.

You should **not** be doing clustering in your code. I adds noise and is right now preventing the script from running unclustered. There are pretty sweet tools to manage your process, bring it back up when it crashes, monitor it and finally cluster it. Tools like [PM2](https://github.com/Unitech/pm2)

What I suggest is to:
- add the `pm2` dependency to the `package.json`
- remove the clustering logic from `app.js`
- change the `npm start` command for `pm2 start app.js -i max` where `max` can easily be changed to any number to define the number of clusters to make.

PM2 also has the advantage to be hookable for remote monitoring with almost no effort, which could be interesting for this project.

Cheers

Empieza leyendo package.json y app.js para entender el comando de inicio actual y la lógica de clustering. Compara la configuración de PM2 solicitada con el comportamiento existente del proceso y, después, verifica que npm start inicie el ejemplo como se especifica y que el clustering ya no se gestione en app.js.

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