Update dependency prom-client to v15

Author: renovate[bot]

25-monitoring-application-with-prometheus/src/quote-svc/package.json

@@ -13,7 +13,7 @@
     "express": "^4.17.1",
     "express-prom-bundle": "^6.0.0",
     "nodemon": "^2.0.4",
-    "prom-client": "^14.0.0",
+    "prom-client": "^15.0.0",
     "random-quote": "0.0.1"
   }
 }