Change babel configuration

[ivmartel]

The current config embeds possible poly-fills with the code when this is the responsibility of the client.

The browserlist configuration does not need to be so large, it can be made narrower to reduce the dist size. The default corresponds to: > 0.5%, last 2 versions, Firefox ESR, not dead (see doc), the percentage can be set to 1%. See effect on https://browsersl.ist/#.