ENYO-1740: update dropbox-js from 0.3.5 to 0.8.1

- From https://github.com/dropbox/dropbox-js, install using npm
- 0.8.1 is written in CoffeScript:  ARES uses only the compiled version

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>