docs(elastic): updates readme

public/app/plugins/datasource/elasticsearch/README.md

-# CloudWatch Datasource -  Native Plugin
+# Elasticsearch Datasource -  Native Plugin
 
 Grafana ships with **advanced support** for Elasticsearch. You can do many types of simple or complex elasticsearch queries to visualize logs or metrics stored in Elasticsearch. You can also annotate your graphs with log events stored in Elasticsearch.
 
 Read more about it here:
 
-[http://docs.grafana.org/datasources/elasticsearch/](http://docs.grafana.org/datasources/elasticsearch/)
\ No newline at end of file
+[http://docs.grafana.org/datasources/elasticsearch/](http://docs.grafana.org/datasources/elasticsearch/)