Update Super Grub 2 location

src/utils.ipxe

@@ -81,8 +81,8 @@ set util_file cd140201.zip
 goto boot_memdisk
 
 :supergrub
-set util_path forja.cenatic.es/frs/download.php/file/1844/super_grub2_disk_hybrid_2.02s3.iso
-set util_file super_grub2_disk_hybrid_2.02s3.iso
+set util_path https://sourceforge.net/projects/supergrub2/files/2.02s4/super_grub2_disk_hybrid_2.02s4.iso/download
+set util_file super_grub2_disk_hybrid_2.02s4.iso
 goto boot_memdisk
 
 :ubcd