Can’t run Felt with SyntaxError on Node v4

自分の環境だけかもしれませんが、うまく動かなかったので・・。
凡ミスだったらすみません。。

I’ve tried to use Felt with just described commands as below.

```
$ npm install -g felt felt-recipe-minimal
$ cd path/to/project/
$ felt
```

But I couldn’t run Felt with these error messages.

```
/Users/youthkee/.nodebrew/node/v4.2.6/lib/node_modules/felt/lib/config-builder.js:20
module.exports = function(...configs) {
^^^

SyntaxError: Unexpected token ...
at exports.runInThisContext (vm.js:53:16)
at Module._compile (module.js:374:25)
at Object.Module._extensions..js (module.js:417:10)
at Module.load (module.js:344:32)
at Function.Module._load (module.js:301:12)
at Module.require (module.js:354:17)
at require (internal/module.js:12:17)
at Object. (/Users/youthkee/.nodebrew/node/v4.2.6/lib/node_modules/felt/bin/index.js:12:19)
at Module._compile (module.js:410:26)
at Object.Module._extensions..js (module.js:417:10)
```

Is there any requirements or settings to use Felt?
My environments are here.

Mac OS X 10.10.5
node v4.2.6 (installed with nodebrew)

Reproduce the failure with the reported npm install and felt commands on Node v4.2.6, then inspect lib/config-builder.js around line 20 and the loading path from bin/index.js. Check the project's supported Node requirements; done means Felt either runs with the stated environment or clearly documents the required settings or version.

Written by the indexing model from the issue text.