colordiff: add archive URL

When a new version of colordiff is released the old tarball is moved to
the archive directory. This breaks builds until the derivation is
updated to the new version. This commit lets fetchurl know about the
archive URL.

pkgs/tools/text/colordiff/default.nix

@@ -4,7 +4,10 @@ stdenv.mkDerivation rec {
   name = "colordiff-1.0.16";
 
   src = fetchurl {
-    url = "http://www.colordiff.org/${name}.tar.gz";
+    urls = [
+      "http://www.colordiff.org/${name}.tar.gz"
+      "http://www.colordiff.org/archive/${name}.tar.gz"
+    ];
     sha256 = "12qkkw13261dra8pg7mzx4r8p9pb0ajb090bib9j1s6hgphwzwga";
   };