don't log 404s to gravatar.com

lib/final_destination.rb

@@ -253,6 +253,9 @@ class FinalDestination
   end
 
   def log(log_level, message)
+    # blacklist 404 on gravatar.com
+    return if @status_code = 404 && @uri.hostname["gravatar.com"]
+
     Rails.logger.public_send(
       log_level,
       "#{RailsMultisite::ConnectionManagement.current_db}: #{message}"