refine the content

@@ -18,9 +18,9 @@ For the wiki for SRS/3.0, please read [Chinese][srs_CN] or [English][srs_EN].
   * [Wiki](#wiki)
 * [Product](#product)
   * [History](#history)
-    * [v3.0](#v3)
-    * [v2.0](#v2)
-    * [v1.0](#v1)
+    * [v3.0 changes](#v3)
+    * [v2.0 changes](#v2)
+    * [v1.0 changes](#v1)
   * [Features](#features)
   * [Releases](#releases)
   * [Compare](#compare)