Elasticsearch: Clarify minimum Gerrit version required for 6.6.x

Elasticsearch 6.6.x is supported from 2.15.10 or 2.16.5.

Change-Id: Ie342819781820138ad496e537e48d9e496c8b77f
diff --git a/pages/site/elasticsearch.md b/pages/site/elasticsearch.md
index 66956c3..cc2e289 100644
--- a/pages/site/elasticsearch.md
+++ b/pages/site/elasticsearch.md
@@ -17,7 +17,7 @@
 | 6.3.x                 | 2.14.10 or 2.15.3      |
 | 6.4.x                 | 2.14.12 or 2.15.4      |
 | 6.5.x                 | 2.15.8 or 2.16.1       |
-| 6.6.x                 | 2.15.10                |
+| 6.6.x                 | 2.15.10 or 2.16.5      |
 
 Note that although Elasticsearch 2.4.x is supported, we do not recommend using
 such an old version.