ivan: add myself as maintainer

maintainers/maintainer-list.nix

···
     github = "fps";
     name = "Florian Paul Schmidt";
   };
+  freepotion = {
+    email = "[e-mail]";
+    github = "freepotion";
+    name = "Free Potion";
+  };
   Fresheyeball = {
     email = "[e-mail]";
     github = "fresheyeball";

pkgs/games/ivan/default.nix

···
     homepage = https://attnam.com/;
     license = licenses.gpl2Plus;
     platforms = platforms.linux;
-    maintainers = with maintainers; [];
+    maintainers = with maintainers; [freepotion];
   };
 }