style(rubocop): Style/GlobalStdStream

lib/postal/config.rb

@@ -96,7 +96,7 @@ module Postal
     @loggers[name.to_sym] ||= begin
       require "postal/app_logger"
       if config.logging.stdout || ENV["LOG_TO_STDOUT"]
-        Postal::AppLogger.new(name, STDOUT)
+        Postal::AppLogger.new(name, $stdout)
       else
         FileUtils.mkdir_p(log_root)
         Postal::AppLogger.new(name, log_root.join("#{name}.log"), config.logging.max_log_files, config.logging.max_log_file_size.megabytes)