fix(open file): set target win when opening new file

fixes #1214
Still this is a patch that is not really great. This code should be
rewritten.

lua/nvim-tree/actions/open-file.lua

@@ -247,6 +247,7 @@ function M.fn(mode, filename)
     cmd = cmd .. vim.fn.fnameescape(filename)
     api.nvim_set_current_win(target_winid)
     pcall(vim.cmd, cmd)
+    lib.set_target_win()
   end
 
   if M.resize_window then