Fix the plugin installation

Change-Id: If4c1893ab7068687f597fa406d4a568af143520b
diff --git a/grafana/server.sls b/grafana/server.sls
index 647f54e..7c66e5c 100644
--- a/grafana/server.sls
+++ b/grafana/server.sls
@@ -84,7 +84,7 @@
 install_{{ plugin_name }}:
   cmd.run:
   - name: grafana-cli plugins install {{ plugin_name }}
-  - unless: grafana-cli plugins list-versions {{ plugin_name }}
+  - unless: grafana-cli plugins ls | grep {{ plugin_name }}
   - watch_in:
     - service: grafana_service
 {%- endif %}