Fix dashboard ID

Change-Id: I750ebadcb266b2fe722bc15dab83f3dedf3bc5c2
diff --git a/heat/files/grafana_dashboards/heat_prometheus.json b/heat/files/grafana_dashboards/heat_prometheus.json
index 2e127ae..debdd50 100644
--- a/heat/files/grafana_dashboards/heat_prometheus.json
+++ b/heat/files/grafana_dashboards/heat_prometheus.json
@@ -7,7 +7,7 @@
   "gnetId": null,
   "graphTooltip": 1,
   "hideControls": false,
-  "id": 18,
+  "id": null,
   "links": [],
   "refresh": "1m",
   "rows": [
@@ -589,4 +589,4 @@
   "title": "Heat",
   "version": 17
 }
-{%- endraw %}
\ No newline at end of file
+{%- endraw %}