fix readme replace error :)

Author: radu-gheorghe

README.md

@@ -6,7 +6,7 @@ opensearch functionality that has been removed from Elasticsearch starting
 from version 6.0. It imitates the old functionality and is compatible with the
 old API.
 
-Read more about potential use cases in the blog post [Field Stats for Elasticsearch 6.x](https://sematext.com/blog/field-stats-plugin-opensearch/).
+Read more about potential use cases in the blog post [Field Stats for Elasticsearch 6.x](https://sematext.com/blog/field-stats-plugin-elasticsearch/).
 
 Installation
 ------------