neovim: Add back nvim-scrollbar

Looks like the issue where the scrollbar was hiding text behind it has
been fixed.

modules/neovim/default.nix

@@ -98,6 +98,11 @@
             plugin = nvim-web-devicons;
             type = "lua";
           }
+          {
+            plugin = nvim-scrollbar;
+            type = "lua";
+            config = ''require("scrollbar").setup()'';
+          }
           {
             plugin = nvim-lspconfig;
             type = "lua";