[Vue warn]: "class" is a reserved attribute and cannot be used as component prop.

It's related to all projects that use https://github.com/paulpflug/vue-mixins/blob/master/src/class.coffee:

```
default.js:7 [Vue warn]: "class" is a reserved attribute and cannot be used as component prop.

found in

---> <Collapsible>
       <ExpressPayment>
         <ExpressTheme>
           <SinglePageCheckout>
             <Root>
```