gracefully handle strings passed to the NumberFormatter

I was getting `undefined is not a function` errors due to my model
number attr being represented as a string. e.g.

```javascript
model.get('count') //-> "33"
```

A simple fix would just be to parseFloat the passed 'number' to ensure
that it is a number.

I don't think there is an issue with this change?
Merge branch 'type-correct-NumberFormatter-input'