Now is working!! (using an internet file) 
Just a little detail. Instead of an internet sound, I want to use a local .mp3 file. So I changed the line from:
observeEvent(input$go, ({
shinyjs::runjs(
"var music = new Howl({src:['http://www.sonidosmp3gratis.com/sounds/mario-coin.mp3'],
autoplay: true});")
})
to this new:
observeEvent(input$go, ({
shinyjs::runjs(
"var music = new Howl({src:['www/tono.mp3'],
autoplay: true});")
})
And in this case, it doesn't work. I don't know why 
Here is the proof that the music file is in the correct folder.
