Routing error when 2fa page on subdomain

[dachinat]

Let's say you have set-up two factor authentication on sub-domain "admin.example.com"

Scenario:
Log-in to get prompted for 2nd factor code
Don't enter your code, navigate to "example.com" without subdomain
You'll get a routing error. Gem tries to show 2nd factor form page.

Possible fix:

Replace path with url in two_factor_authentication/controllers/helpers.rb:33

change_path = "#{scope}_two_factor_authentication_url"

[dachinat]

This PR solves such issues in a different way #157