Remove “/..” from root directory if “restrict_above_cwd” is enabled

[davilera]

Currently, nvim-tree’s default behavior is to append /.. to the root directory. This makes sense because the user can't browse one directory up. However, if actions.change_dir.restrict_above_cwd is enabled, this is no longer possible.

Therefore, I'd recommend appending /.. in local function format_root_name if, and only if, actions.change_dir.restrict_above_cwd is not enabled. IMO, this would result in a better UX.

[alex-courtis]

Added feature request #1743