Fix broken link_to route

[patcon]

https://github.com/18F/identity-idp/blob/master/app/views/verify/activated.html.slim#L6

This route idv_url no longer exists, and so an error is thrown. Seems it was changed to verify_url, but that would result in a loop on this page, so I'm not sure what it should be ;)

[jessieay]

Fixed this here: #899

Not sure why we don't have any feature specs that hit the "activated" page... I added a view spec but it seems like one of our feature specs should have caught this sooner.

Thanks for reporting!