fix: Outline auto-update

- Typo in checking for buflisted.
- As it turns out bufhidden isn't boolean, so let's not even consider it
  for now. Doing this still allows buffers like LspInfo to be ignored,
  it seems. In the future we will have configurable ignored buffers.

Thanks to @Djedouas for bringing it up.

lua/outline/sidebar.lua

@@ -334,9 +334,8 @@ function Sidebar:__refresh()
     return
   end
   local ft = vim.api.nvim_buf_get_option(buf, 'ft')
-  local nolisted = vim.api.nvim_buf_get_option(buf, 'buflisted')
-  local hidden = vim.api.nvim_buf_get_option(buf, 'bufhidden')
-  if ft == 'OutlineHelp' or nolisted or hidden then
+  local listed = vim.api.nvim_buf_get_option(buf, 'buflisted')
+  if ft == 'OutlineHelp' or not listed then
     return
   end
   self.provider = providers.find_provider()