updated node stats API call to support ES 1.x

In version 1.0 a breaking change was introduced to the node stats portion of the cluster apis. 

What was previously `ES_HOST/_cluster/nodes/stats?all=true` is now `ES_HOST/_nodes/stats?all=true`

0.9x - http://www.elasticsearch.org/guide/en/elasticsearch/reference/0.90/cluster-nodes-stats.html

1.x - http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/cluster-nodes-stats.html

@mattweber