[docs] Set sort upgrade pages

Author: andrey-helldar

docs/do.tree

@@ -8,7 +8,7 @@
 
     <toc-element toc-title="Prologue">
         <toc-element topic="introduction.topic" />
-        <toc-element toc-title="Upgrade Guide">
+        <toc-element toc-title="Upgrade Guide" sort-children="descending">
             <toc-element topic="upgrade-7.topic" toc-title="Upgrade to 7.x" />
             <toc-element topic="upgrade-6.topic" toc-title="Upgrade to 6.x" />
             <toc-element topic="upgrade-5.topic" toc-title="Upgrade to 5.x" />