Merge branch 'atomaka/bugfix/staging-api' into 'master'

Allow api subdomain on staging to work too

in staging, the subdomain becomes 'api.staging' and 'api' will not match. We can resolve this with a regex: `/^api(\.|$)/`.

There is a configuration setting, `config.action_dispatch.tld_length` that could resolve this as well.  Typically, I imagine this being set by environment, but since Heroku suggests running all Rails apps as production, even if it is a different environment, this isn't really an option.

See merge request !24

config/routes.rb

@@ -29,7 +29,7 @@ Rails.application.routes.draw do
     resources :versions, only: [:show]
   end
 
-  constraints subdomain: 'api' do
+  constraints subdomain: /^api(\.|$)/ do
     namespace :api, path: nil do
       namespace :v1 do
         resources :cards, only: [:index, :show]