charybdis: use new homepage link

pkgs/servers/irc/charybdis/default.nix

···
 
   meta = with stdenv.lib; {
     description = "IRCv3 server designed to be highly scalable";
-    homepage    = http://www.charybdis.io/;
+    homepage    = http://atheme.org/projects/charybdis.html;
     license     = licenses.gpl2;
     maintainers = with maintainers; [ lassulus fpletz ];
     platforms   = platforms.unix;