mingw-w64: Fix typo in preConfigure hook.

D'oh, no wonder the headers are of almost the same size as the main
package.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/os-specific/windows/mingw-w64/default.nix

@@ -13,7 +13,7 @@ stdenv.mkDerivation (rec {
 } //
 (if onlyHeaders then {
   name = name + "-headers";
-  preConfingure = ''
+  preConfigure = ''
     cd mingw-w64-headers
   '';
   configureFlags = "--without-crt --host=x86_64-w64-mingw32";