Null logging should not print anything to STDOUT (#381)

src/kemal/null_log_handler.cr

@@ -2,7 +2,6 @@ module Kemal
   # This is here to represent the logger corresponding to Null Object Pattern.
   class NullLogHandler < Kemal::BaseLogHandler
     def call(context)
-      puts "This is null"
       call_next(context)
     end