d4x: Update download URL to fedora, d4k.krasu.ru no longer exists

(cherry picked from commit 2c8cb42c7148f861a7d8d60ca766f47ed7c1d90d)

pkgs/applications/misc/d4x/default.nix

···
   inherit boost;
 
   src = fetchurl {
-    url =  http://d4x.krasu.ru/files/d4x-2.5.7.1.tar.bz2;
+    url = http://pkgs.fedoraproject.org/repo/pkgs/d4x/d4x-2.5.7.1.tar.bz2/68d6336c3749a7caabb0f5a5f84f4102/d4x-2.5.7.1.tar.bz2;
     sha256 = "1i1jj02bxynisqapv31481sz9jpfp3f023ky47spz1v1wlwbs13m";
   };