package.json: re-add npm as 'engine' (Heroku)
package.json: use latest maintenance release of 0.8.x nodejs
Remove .buildpacks (we'll use https://github.com/olragon/heroku-buildpack-nodejs)

see comment by olragon @ http://stackoverflow.com/a/14411015
Use latest node+npm
Add buildpacks (http://stackoverflow.com/a/14060619/857721)