Turn more licenses into lib.licenses style

Should eval cleanly, as far as -A tarball tells me.

Relevant: issue #2999, issue #739

pkgs/tools/X11/xdg-utils/default.nix

@@ -2,7 +2,7 @@
 
 stdenv.mkDerivation rec {
   name = "xdg-utils-1.1.0-rc1";
-  
+
   src = fetchurl {
     url = "http://portland.freedesktop.org/download/${name}.tar.gz";
     sha256 = "00lisw4x43sp189lb7dz46j2l09y5v2fijk3d0sxx3mvwj55a1bv";
@@ -11,11 +11,11 @@ stdenv.mkDerivation rec {
   postInstall = ''
     substituteInPlace $out/bin/xdg-mime --replace /usr/bin/file ${file}/bin/file
   '';
-  
+
   meta = {
     homepage = http://portland.freedesktop.org/wiki/;
     description = "A set of command line tools that assist applications with a variety of desktop integration tasks";
-    license = "free";
+    license = stdenv.lib.licenses.free;
     maintainers = [ stdenv.lib.maintainers.eelco ];
     platforms = stdenv.lib.platforms.linux;
   };