[WEBSITE] Items webpage has broken filtering

Filtering on items that only appear on Summoner's Rift returns no results.

Steps to reproduce:

1. Visit webpage. Note all items are listed.
2. Click "Twisted Treeline" checkbox on the right. Note only TT items show up.
3. Uncheck "Twisted Treeline". Note all items return.
4. Check "Summoner's Rift". Note that no items are returned.