libtiger: add license meta

pkgs/development/libraries/libtiger/default.nix

@@ -16,6 +16,7 @@ stdenv.mkDerivation rec {
     homepage = https://code.google.com/archive/p/libtiger/;
     description = "A rendering library for Kate streams using Pango and Cairo";
     platforms = lib.platforms.unix;
+    license = lib.licenses.lgpl21Plus;
     maintainers = with lib.maintainers; [ matthewbauer ];
   };
 }