beast: switch to a working src location, fixes #9936

It also needs an update, it seems, but I don't know this SW.

pkgs/applications/audio/beast/default.nix

···
 { stdenv, fetchurl, zlib, guile, libart_lgpl, pkgconfig, intltool
 , gtk, glib, libogg, libvorbis, libgnomecanvas, gettext, perl }:
 
-stdenv.mkDerivation {
+stdenv.mkDerivation rec {
   name = "beast-0.7.1";
 
   src = fetchurl {
-    url = ftp://beast.gtk.org/pub/beast/v0.7/beast-0.7.1.tar.bz2;
+    url = "http://ftp.gtk.org/pub/beast/v0.7/${name}.tar.bz2";
     sha256 = "0jyl1i1918rsn4296w07fsf6wx3clvad522m3bzgf8ms7gxivg5l";
   };