Fix telegraf configuration

Change-Id: I260b1c616b0791a91798fe9416e48bf8cc5446e9
diff --git a/nginx/files/telegraf.conf b/nginx/files/telegraf.conf
index e792f04..2a5ad25 100644
--- a/nginx/files/telegraf.conf
+++ b/nginx/files/telegraf.conf
@@ -1,2 +1,2 @@
 [[inputs.nginx]]
-  urls = {{ values.urls|json }}
\ No newline at end of file
+  urls = {%- if values.urls is string %}[ "{{ values.urls }}" ]{%- else %}{{ values.urls|json }}{%- endif %}