Add Searchkick::Results#entry_name method for kaminari compatibility

From [kaminari 0.16.0](https://github.com/amatsuda/kaminari/releases/tag/v0.16.0) (more specifically from this commit: https://github.com/amatsuda/kaminari/commit/507fb73b09475a0efbd99d0398bf4a3c9632ca18), `#page_entries_info` requires paginatable objects to have `#entry_name` method. `SearchKick::Results` should also have it so it'll play nice together with kaminari.