Fix processes_zombies metric name

Change-Id: Ic92564d97000c8bbb824a678af0c9cb7521eaa7e
diff --git a/linux/files/grafana_dashboards/system_prometheus.json b/linux/files/grafana_dashboards/system_prometheus.json
index da11d16..a3910a2 100755
--- a/linux/files/grafana_dashboards/system_prometheus.json
+++ b/linux/files/grafana_dashboards/system_prometheus.json
@@ -538,7 +538,7 @@
               "step": 10
             },
             {
-              "expr": "processes_zombie{host=\"$host\"}",
+              "expr": "processes_zombies{host=\"$host\"}",
               "format": "time_series",
               "intervalFactor": 2,
               "legendFormat": "zombie",