非推奨になっていたため

log4js-node/log4js-node#1080
```
(node:38719) [streamroller-DEP0001] DeprecationWarning: options.daysToKeep is deprecated due to the confusion it causes when used together with file size rolling. Please use options.numBackups instead.
```

ssr-server/src/log/config.js

@@ -38,7 +38,7 @@ export const log4jsConfig = {
       layout: logLayout,
       filename: path.join(logDirectory, "app.log"),
       pattern: "-yyyy-MM-dd",
-      daysToKeep: 7,
+      numBackups: 7,
       compress: true,
     },
   },