Fix documentation for CreateMergePatchSetForChange REST API endpoint.

Change-Id: Ifcd9b8560e9bca2187669a4e7127818e78b6830a
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 903acc7..6722824 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -536,7 +536,10 @@
   Content-Type: application/json; charset=UTF-8
 
   {
-    "source": "refs/12/1234/1"
+    "subject": "Merge dev_branch into master",
+    "merge": {
+      "source": "refs/12/1234/1"
+    }
   }
 ----