dvdisaster: fix $out variable expansion (makeFlags)

Make requires variables with more than one letter to be surrounded by parentheses,
like `$(out)`. Just writing `$out` will be interpreted as `$o` followed by `ut`, so
the package installed its documentaion to `ut/share/doc`.

/cc maintainers @jgeerds @nckx

pkgs/tools/cd-dvd/dvdisaster/default.nix

@@ -30,7 +30,7 @@ stdenv.mkDerivation rec {
 
   configureFlags = [
     # Explicit --docdir= is required for on-line help to work:
-    "--docdir=$out/share/doc"
+    "--docdir=share/doc"
     "--with-nls=yes"
     "--with-embedded-src-path=no"
   ] ++ stdenv.lib.optional (builtins.elem stdenv.system