shotcut: Fix running of {pre,post}Configure

Commit 0055c6a introduced a new preConfigure hook that sets the right
qmake path. Unfortunately the mkDerivation attributes of shotcut
override the whole configurePhase, so this hook isn't run at all.

However, this still doesn't fix the package and its already marked as
broken.

The build fails with the following error:

Project ERROR: Unknown module(s) in QT: qml quick webkitwidgets x11extras

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

pkgs/applications/video/shotcut/default.nix

@@ -11,7 +11,11 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ SDL frei0r gettext makeWrapper mlt pkgconfig qtbase ];
 
-  configurePhase = "qmake PREFIX=$out";
+  configurePhase = ''
+    runHook preConfigure
+    qmake PREFIX=$out
+    runHook postConfigure
+  '';
 
   postInstall = ''
     mkdir -p $out/share/shotcut