Merge pull request #19 from metrics-js/renovate/prom-client-12.x

Dev dependency update: prom-client

Author: trygve-lie

package.json

@@ -39,6 +39,6 @@
     "eslint-plugin-import": "2.20.0",
     "benchmark": "2.1.4",
     "tap": "14.10.6",
-    "prom-client": "11.5.3"
+    "prom-client": "12.0.0"
   }
 }