tensor: fix darwin build

pkgs/applications/networking/instant-messengers/tensor/default.nix

@@ -1,4 +1,5 @@
-{ mkDerivation, lib, fetchgit, qtbase, qtquickcontrols, qmake, makeDesktopItem }:
+{ mkDerivation, lib, stdenv, fetchgit, qtbase, qtquickcontrols, qmake
+, makeDesktopItem }:
 
 # we now have libqmatrixclient so a future version of tensor that supports it
 # should use that
@@ -30,7 +31,15 @@ mkDerivation rec {
     mimeType    = "application/x-chat";
   };
 
-  installPhase = ''
+  installPhase = if stdenv.isDarwin then ''
+    runHook preInstall
+
+    mkdir -p $out/Applications
+    cp -r tensor.app $out/Applications/tensor.app
+    wrapQtApp $out/Applications/tensor.app/Contents/MacOS/tensor
+
+    runHook postInstall
+  '' else ''
     runHook preInstall
 
     install -Dm755 tensor $out/bin/tensor