nvim: switch undotree for telescope-undo-nvim

Undotree did not have live updates like I wanted, so I have switched to
the telescope one which does.

packages/default.nix

@@ -115,10 +115,10 @@ in
               nvim-lspconfig
               spaceman-nvim
               telescope-nvim
+              telescope-undo-nvim
               toggleterm-nvim
               tokyonight-nvim
               typst-vim
-              undotree
               vim-lsp-cxx-highlight
               which-key-nvim
             ];