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

app/controllers/clicks_controller.rb

@@ -1,6 +1,6 @@
 class ClicksController < ApplicationController
 
-  skip_before_filter :check_xhr, :preload_json
+  skip_before_action :check_xhr, :preload_json
 
   def track
     raise Discourse::NotFound unless params[:url]
@@ -15,7 +15,7 @@ class ClicksController < ApplicationController
     # Sometimes we want to record a link without a 302. Since XHR has to load the redirected
     # URL we want it to not return a 302 in those cases.
     if params[:redirect] == 'false' || @redirect_url.blank?
-      render nothing: true
+      render body: nil
     else
       redirect_to(@redirect_url)
     end