$.data doesn't work when hyphen is used

This will not work
```pug
div(data-animal-type='dragon')
```
```js
$('div').data('animal-type'); // undefined
```

This will work
```pug
div(data-animaltype='dragon')
```
```js
$('div').data(animaltype); // dragon
```

I think animal-type should work since we see alot of hyphens in HTML documents and is in the spec as well