fixed

app/controllers/admin/application_controller.rb

@@ -1,5 +1,3 @@
-module Admin
-  class ApplicationController < ApplicationController
-    http_basic_authenticate_with name: 'admin', password: ENV['ADMIN_PASSWORD'] unless Rails.env.development?
-  end
+class Admin::ApplicationController < ApplicationController
+  http_basic_authenticate_with name: 'admin', password: ENV['ADMIN_PASSWORD'] unless Rails.env.development?
 end

app/controllers/admin/pages_controller.rb

@@ -1,4 +1,4 @@
-class PagesController < Admin::ApplicationController
+class Admin::PagesController < Admin::ApplicationController
   def map
     @supporters = Supporter.where(:coordinates.ne => nil).only(:coordinates, :support)
   end

app/controllers/admin/supporters_controller.rb

@@ -1,4 +1,4 @@
-class SupportersController < Admin::ApplicationController
+class Admin::SupportersController < Admin::ApplicationController
   def index
     @supporters = Supporter.desc(:created_at)
   end