Updated the ES versioning

Author: ezimuel

README.md

@@ -29,8 +29,7 @@ Version Matrix
 
 | Elasticsearch Version | Elasticsearch-PHP Branch |
 | --------------------- | ------------------------ |
-| >= 6.6, <= 6.7        | 6.7                      |
-| >= 6.0, <= 6.5        | 6.5                      |
+| >= 6.0, < 7.0         | 6.0                      |
 | >= 5.0, < 6.0         | 5.0                      |
 | >= 2.0, < 5.0         | 1.0 or 2.0               |
 | >= 1.0, < 2.0         | 1.0 or 2.0               |