Build NOVA in parallel

The current hydra build time is in excess of ten seconds, this is
unacceptable.

NOVA/default.nix

@@ -23,6 +23,8 @@ buildPackages.stdenv.mkDerivation {
     sha256 = "0rkp59496032kq8a3l5fs771m5f7s5yywkxjk7j9qhmsidgk40wd";
   };
 
+  enableParallelBuilding = true;
+
   makeFlags = [ "--directory=build" ];
 
   preInstall = "export INS_DIR=$out";