haskell-ghc-mod: Correct patch to ghc-process.el

This change has been accepted upstream, so soon it will not be necessary.

pkgs/development/libraries/haskell/ghc-mod/default.nix

@@ -21,7 +21,7 @@ cabal.mkDerivation (self: {
   configureFlags = "--datasubdir=${self.pname}-${self.version}";
   postInstall = ''
     cd $out/share/$pname-$version
-    sed -i -e 's/"-b" "\\n" "-l"/"-l" "-b" "\\"\\\\n\\""/' ghc-process.el
+    sed -i -e 's/"-b" "\\n" "-l"/"-l" "-b" "\\"\\n\\""/' ghc-process.el
     make
     rm Makefile
     cd ..