attempt to make the log directory if missing

lib/postal/config.rb

@@ -86,6 +86,7 @@ module Postal
       if config.logging.stdout || ENV['LOG_TO_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)
       end
     end