Gruntfile: update to modern JS
Gruntfile: update to modern JS

j5js/johnny-five.io,johnny-five-io/johnny-five.io,j5js/johnny-five.io,johnny-five-io/johnny-five.io,bocoup/johnny-five.io,johnny-five-io/johnny-five.io,bocoup/johnny-five.io,bocoup/johnny-five.io,j5js/johnny-five.io