Fix all the errors to get our tests green on Rails 5.1.

app/controllers/admin/admin_controller.rb

@@ -1,10 +1,10 @@
 class Admin::AdminController < ApplicationController
 
-  before_filter :ensure_logged_in
-  before_filter :ensure_staff
+  before_action :ensure_logged_in
+  before_action :ensure_staff
 
   def index
-    render nothing: true
+    render body: nil
   end
 
 end