Merge pull request #505 from jupyterhub/dependabot/npm_and_yarn/prom-client-15.0.0

Author: dependabot[bot]

package-lock.json

@@ -11,7 +11,7 @@
   "dependencies": {
     "commander": "~7.2",
     "http-proxy": "^1.18.1",
-    "prom-client": "14.2.0",
+    "prom-client": "15.0.0",
     "strftime": "~0.10.0",
     "winston": "~3.11.0"
   },