Make use of `keys` in `vals` keeping the code DRYer

Using `exports.keys` to get all defined keys on the object. Reusing the returned array to store the object values. 

I don't really know how many browsers you want to cover but when you assume that `Array.map` is supported than the `vals` function could be written as:

```js
exports.vals = function (object){
  return exports.keys(object).map(function(key){ 
    return object[key]; 
  };
}
```