Update node.js buildpack for io.js support

[silverwind]

Hopefully this is the correct repo to file this against.

Using dokku 0.3.16, it seems the detection of engines.iojs in package.json isn't working and it falls back to node.js:

-----> Node.js app detected

       PRO TIP: Specify a node version in package.json
       See https://devcenter.heroku.com/articles/nodejs-support

-----> Defaulting to latest stable node: 0.12.2

This feature has been working on official Heroku since around February, maybe the buildpack used here or by dokku is outdated?

[silverwind]

The heroku pack seems to include the check. I've tried to rebuild buildstep as well as setting a custom repo in .env, no luck so far.

Again, sorry if this is the wrong repo.

[silverwind]

Sorted it out by adding

export BUILDPACK_URL=https://github.com/heroku/heroku-buildpack-nodejs

in ~/ENV. Quite hard to discover stuff like this.