Setting width to 100% throws warning

I want the chart to fill the parent element, so I set the width to 100% as per the JUI chart docs:
```html
<graph-bar width="100%"...
```
While this works fine, the console shows the following error:
```
[Vue warn]: Invalid prop: type check failed for prop "width". Expected Number, got String.
```
Note, this is not using bind.