Change `search_text` to use `option.text` rather than `option.html`

Ember.js litters the DOM with <script> tags to perform its DOM binding. So when using an `Ember.Select` component with Chosen, searches would never return results because the regex binds to the start using `/^...`, and `option.html` starts with a <script> tag.

This PR fixes the problem by searching on `option.text`. Another solution would be to change the regex to not bind to the start, but these seemed to be a less significant change.