Add GRBurst as maintainer

lib/maintainers.nix

···
   goodrone = "Andrew Trachenko <[e-mail]>";
   gpyh = "Yacine Hmito <[e-mail]>";
   grahamc = "Graham Christensen <[e-mail]>";
+  grburst = "Julius Elias <[e-mail]>";
   gridaphobe = "Eric Seidel <[e-mail]>";
   guibert = "David Guibert <[e-mail]>";
   guillaumekoenig = "Guillaume Koenig <[e-mail]>";