[ais-pagination] CSS classes are added twice for `ais-pagination_item`

[pixelastic]

Do you want to request a feature or report a bug?
Bug

Bug: What is the current behavior?
When specifying custom classes for ais-pagination__item, classes are added twice to the element.

Bug: What is the expected behavior?
Classes should be added only once.

The issue can be seen live at https://codepen.io/anon/pen/VMxaqZ

<ais-pagination v-bind:class-names="{'ais-pagination__item': 'foo bar baz'}"></ais-pagination>

The bug seem to occur whichever element is selected (first, last, any in the list).

It's not critical, as two CSS classes applied to the same element won't generate too much trouble, but I'd rather report it :)

[pixelastic]

Thanks for the quick fix \o/