docs/extension-point: use consistent heading markup

This style of heading markup is more prevalent in these docs. This also
corrects the heading levels, since level two was skipped before.

Change-Id: I2e2e020aa23b541aa4b02a8b9ce45bb8082aaa70

src/main/resources/Documentation/extension-point.md

diff --git a/src/main/resources/Documentation/extension-point.md b/src/main/resources/Documentation/extension-point.md
index dc757ba..f6579fa 100644
--- a/src/main/resources/Documentation/extension-point.md
+++ b/src/main/resources/Documentation/extension-point.md
@@ -1,11 +1,12 @@
 @PLUGIN@ extension points
-==============
+=========================
 
 The replication plugin exposes an extension point to allow influencing its behaviour from another plugin or a script.
 Extension points can be defined from the replication plugin only when it is loaded as [libModule](../../../Documentation/config-gerrit.html#gerrit.installModule) and
 implemented by another plugin by declaring a `provided` dependency from the replication plugin.
 
-### Install extension libModule
+Install extension libModule
+---------------------------
 
 The replication plugin's extension points are defined in the `c.g.g.p.r.ReplicationExtensionPointModule`
 that needs to be configured as libModule.
@@ -22,8 +23,8 @@
 
 > **NOTE**: Use and configuration of the replication plugin as library module requires a Gerrit server restart and does not support hot plugin install or upgrade.
 
-
-### Extension points
+Extension points
+----------------
 
 * `com.googlesource.gerrit.plugins.replication.ReplicationPushFilter`