support for node 0.12

[cuongluu8]

The package.json suggests this should work with "node": ">= 0.8.0". I'm using 0.12 at the moment and get the following error

Warning: /Users/luuc04/morph/morph-modules/comments-view/node_modules/grunt-cucumberjs/node_modules/cucumber-html-reporter/node_modules/fs-extra/lib/index.js:3
const assign = require('./util/assign')
^^^^^
Use of const in strict mode. Use --force to continue.

I'm not using the default html format (using pretty format), so should it still be trying to load this module?