Fix index markers.

Author: rouilj

doc/upgrading.txt

@@ -30,7 +30,7 @@ Contents:
 .. contents::
    :local:
 
-.. index:: Upgrading; 2.0.0 to 2.1.0
+.. index:: Upgrading; 2.1.0 to 2.2.0
 
 Migrating from 2.1.0 to 2.2.0
 =============================
@@ -248,6 +248,8 @@ jinja2 code with::
   {% endif %}
 
 
+.. index:: Upgrading; 2.0.0 to 2.1.0
+
 Migrating from 2.0.0 to 2.1.0
 =============================