Many properties such as `group`, `filter` and many more should be `type: String` but instead are identified as `Number`. I guess [my check](https://github.com/myfrom/polymer-sortablejs/blob/91eb627562543d32462c0225d719b983bec56314/build.js#L146) doesn't work. ````javascript else if (Number(value) !== NaN) type = 'Number' ````