fix typo in example config

config.example.json

@@ -4,5 +4,5 @@
   "HASTIC_WEBHOOK_URL": "http://localhost:8080",
   "HASTIC_WEBHOOK_TYPE": "application/x-www-form-urlencoded",
   "HASTIC_WEBHOOK_SECRET": "mysecret",
-  "GRAFANA_URL": "http://localhost:3000/"
+  "GRAFANA_URL": "http://localhost:3000"
 }