gxneur: add licenses

pkgs/applications/misc/gxneur/default.nix

···
     libglade GConf pcre libappindicator-gtk2
   ];
 
-  meta = {
+  meta = with stdenv.lib; {
     description = "GUI for XNEUR keyboard layout switcher";
-    platforms = stdenv.lib.platforms.linux;
+    platforms = platforms.linux;
+    license = with licenses; [ gpl2 gpl3 ];
   };
 }