vimPlugins.playground: fix missing dependency

I just spent too much time trying to understand why the query editor woudn't work when the solution was just to install the query grammar, see nvim-treesitter/playground#88 (comment)

pkgs/applications/editors/vim/plugins/overrides.nix

@@ -729,6 +729,13 @@ self: super: {
 
   inherit parinfer-rust;
 
+  playground = super.playground.overrideAttrs (old: {
+    dependencies = with self; [
+      # we need the 'query' grammer to make
+      (nvim-treesitter.withPlugins (p: [ p.query ]))
+    ];
+  });
+
   plenary-nvim = super.plenary-nvim.overrideAttrs (old: {
     postPatch = ''
       sed -Ei lua/plenary/curl.lua \