tela-icon-theme: switch to gpl3Only

Since the license isn't documented anywhere other than COPYING, it must
be assumed that the intent was to license only under the included
license, without any extra clauses such as the "(at your option) any
later version" clause.

pkgs/data/icons/tela-icon-theme/default.nix

@@ -35,7 +35,7 @@ stdenv.mkDerivation rec {
   meta = with lib; {
     description = "A flat colorful Design icon theme";
     homepage = "https://github.com/vinceliuice/tela-icon-theme";
-    license = licenses.gpl3Plus;
+    license = licenses.gpl3Only;
     platforms = platforms.unix;
     maintainers = with maintainers; [ figsoda ];
   };