Fix console errors when entering birth date

[bklang]

Resolves this error:

Assertion Failed: {{power-select}} If you want the default filtering to work on options that are not plain strings, you need to provide `searchField`

The problem is that the search field is expecting strings, but we are passing numbers. This is documented as a requirement by Ember in the section "Customizing the search field"

[bklang]

Putting this one on hold. I've only been able to show the issue in local dev. For some reason, it is not appearing in the staging environment. I'll hold off shipping this unless/until we see it in staging.

[haydenrou]

@bklang I totally didn't see this PR until now and made the same change here! Let me know if you want me to revert it in that PR. I don't see turning these to a string hurting however if there is no need to then I guess we can revert it.

[bklang]

We'll include this with @haydenrou 's work. Closing.