Fix asciidoctor warning in config-gerrit

Change-Id: Icc557fb422ac10cd8cfb9eaffd25a6692bc655e6

Documentation/config-gerrit.txt

diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index a408e75..36a5c5d 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -2742,7 +2742,7 @@
 +
 Defaults to `5 m`
 
-===== Elasticsearch server(s) configuration
+==== Elasticsearch server(s) configuration
 
 Each section correspond to one Elasticsearch server.