Upgrade to webpack 2

[TheLarkInn]

I'd be happy to help get this example updated to webpack 2! This will leverage some great tree shaking support native to webpack two.

[yyx990803]

Well, I should probably label this one as outdated - the 2.0 version does use Webpack 2: https://github.com/vuejs/vue-hackernews-2.0