Fix broken linking in rest-api-changes docs page.

The section was opened and closed with different amount of '-' causing
the linking on the page to break.

Release-Notes: skip
Change-Id: Ic8406552f7a82573860960fa97910e20ef600eeb
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 5a2fc2e..0a913d8 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -382,7 +382,7 @@
 [[custom-keyed-values]]
 --
 * `CUSTOM_KEYED_VALUES`: include the custom key-value map
----
+--
 
 [[star]]
 --