fix(package): update prom-client to version 12.0.0

Closes #43

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
         "body-parser": "~1.19.0",
         "debug": "~4.1.1",
         "express": "~4.16.4",
-        "prom-client": "~11.3.0",
+        "prom-client": "~12.0.0",
         "sinek": "~7.29.3"
     },
     "devDependencies": {