swiften: format the expression

pkgs/development/libraries/swiften/default.nix

@@ -13,15 +13,8 @@ stdenv.mkDerivation rec {
   pname = "swiften";
   version = "4.0.2";
 
-  nativeBuildInputs = [ sconsPackages.scons_3_1_2 ];
-  buildInputs = [
-    python
-    expat
-  ];
-  propagatedBuildInputs = [ openssl boost ];
-
   src = fetchurl {
-    url    = "https://swift.im/downloads/releases/swift-${version}/swift-${version}.tar.gz";
+    url = "https://swift.im/downloads/releases/swift-${version}/swift-${version}.tar.gz";
     sha256 = "0w0aiszjd58ynxpacwcgf052zpmbpcym4dhci64vbfgch6wryz0w";
   };
 
@@ -38,6 +31,20 @@ stdenv.mkDerivation rec {
     })
   ];
 
+  nativeBuildInputs = [
+    sconsPackages.scons_3_1_2
+  ];
+
+  buildInputs = [
+    python
+    expat
+  ];
+
+  propagatedBuildInputs = [
+    openssl
+    boost
+  ];
+
   sconsFlags = [
     "openssl=${openssl.dev}"
     "boost_includedir=${boost.dev}/include"
@@ -48,18 +55,20 @@ stdenv.mkDerivation rec {
     "debug=0"
     "swiften_dll=1"
   ];
-  preInstall = ''
-    installTargets="$out"
-    installFlags+=" SWIFTEN_INSTALLDIR=$out"
-  '';
+
+  installTargets = "${placeholder "out"}";
+
+  installFlags = [
+    "SWIFTEN_INSTALLDIR=${placeholder "out"}"
+  ];
 
   enableParallelBuilding = true;
 
   meta = with lib; {
     description = "An XMPP library for C++, used by the Swift client";
-    homepage    = "http://swift.im/swiften.html";
-    license     = licenses.gpl2Plus;
-    platforms   = platforms.linux;
+    homepage = "http://swift.im/swiften.html";
+    license = licenses.gpl2Plus;
+    platforms = platforms.linux;
     maintainers = [ maintainers.twey ];
   };
 }