Update site address of Snowball project

doc/src/sgml/textsearch.sgml

@@ -2703,7 +2703,7 @@ SELECT ts_lexize('norwegian_ispell', 'sjokoladefabrikk');
     The <application>Snowball</> dictionary template is based on a project
     by Martin Porter, inventor of the popular Porter's stemming algorithm
     for the English language.  Snowball now provides stemming algorithms for
-    many languages (see the <ulink url="http://snowball.tartarus.org">Snowball
+    many languages (see the <ulink url="http://snowballstem.org/">Snowball
     site</ulink> for more information).  Each algorithm understands how to
     reduce common variant forms of words to a base, or stem, spelling within
     its language.  A Snowball dictionary requires a <literal>language</>