libjson-rpc-cpp: enable parallel building

pkgs/development/libraries/libjson-rpc-cpp/default.nix

@@ -56,6 +56,8 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ pkgconfig ];
   buildInputs = [ cmake jsoncpp argtable curl libmicrohttpd doxygen catch ];
 
+  enableParallelBuilding = true;
+
   meta = with stdenv.lib; {
     description = "C++ framework for json-rpc (json remote procedure call)";
     homepage = https://github.com/cinemast/libjson-rpc-cpp;