ngspice: rename pkgname (s/ng-spice-rework/ngspice/)

I think the previous name comes from the fact that some older versions
were distributed in tarballs named ng-spice-rework-<version>. But now
the "rework" name seems odd; most references I found on the internet
calls the package "ngspice". Fix it.

pkgs/applications/science/electronics/ngspice/default.nix

···
 {stdenv, fetchurl, readline, bison, libX11, libICE, libXaw, libXext}:
 
 stdenv.mkDerivation {
-  name = "ng-spice-rework-25";
+  name = "ngspice-25";
 
   src = fetchurl {
     url = "mirror://sourceforge/ngspice/ngspice-25.tar.gz";