Set target window whenever we open "open" a visible tree (#1080)

lua/nvim-tree.lua

@@ -41,6 +41,7 @@ end
 function M.open(cwd)
   cwd = cwd ~= "" and cwd or nil
   if view.is_visible() then
+    lib.set_target_win()
     view.focus()
   else
     lib.open(cwd)