Add linebreak to end of logstash records.

src/Monolog/Formatter/LogstashFormatter.php

@@ -93,6 +93,6 @@ class LogstashFormatter extends NormalizerFormatter
             $message['@fields'][$this->contextPrefix . $key] = $val;
         }
 
-        return json_encode($message);
+        return json_encode($message) . PHP_EOL;
     }
 }