Fixed a minor error in some index file

Author: javiereguiluz

cookbook/map.rst.inc

@@ -110,7 +110,7 @@
 * :doc:`/cookbook/install/index`
 
   * :doc:`/cookbook/install/upgrading`
-  * :doc:`/cookbook/install/unstable_version`
+  * :doc:`/cookbook/install/unstable_versions`
 
 * :doc:`/cookbook/logging/index`