Change stats NOT IMPLEMENTED for unfinished methods

src/main.ts

@@ -54,14 +54,14 @@ class Server {
       const subscription = req.body as Subscription;
       console.log(subscription);
 
-      res.status(201).send();
+      res.status(501).send();
     });
 
     this.app.post('/mute', async (req: Request, res: Response) => {
       const subscription = req.body as Subscription;
       console.log(subscription);
 
-      res.status(201).send();
+      res.status(501).send();
     });
 
     this.app.get('/vapid', async (_: Request, res: Response) => {