docs: update ltree URL for the DMOZ catalog

Reported-by: bbrincat@gmail.com

Discussion: https://postgr.es/m/152283596377.1441.11672249301622760943@wrigleys.postgresql.org

Author: Oleg Bartunov

Backpatch-through: 9.3

doc/src/sgml/ltree.sgml

@@ -34,7 +34,7 @@
    length of a label path must be less than 65kB, but keeping it under 2kB is
    preferable.  In practice this is not a major limitation; for example,
    the longest label path in the DMOZ catalog (<ulink
-   url="http://www.dmoz.org"></ulink>) is about 240 bytes.
+   url="http://www.dmoztools.net"></ulink>) is about 271 bytes.
   </para>
 
   <para>