FIX: apply defaults constraints to routes format (#7890)

This fixes the problem where if a route ends with a dynamic segment and the segment contains a period e.g. `my.name`, `name` is interpreted as the format. This applies a default format constraints `/(json|html)/` on all routes. If you'd like a route to have a different format constraints, you can do something like this:

```ruby
get "your-route" => "your_controlller#method", constraints: { format: /(rss|xml)/ }

#or
get "your-route" => "your_controlller#method", constraints: { format: :xml }
```

app/controllers/users_controller.rb

@@ -1065,7 +1065,10 @@ class UsersController < ApplicationController
       @confirmed = true
     end
 
-    render layout: 'no_ember'
+    respond_to do |format|
+      format.json { render json: success_json }
+      format.html { render layout: 'no_ember' }
+    end
   end
 
   def list_second_factors