fix(#2157): use stdpath cache for nvim-tree-on-attach.lua (#2159)

* fix(#2157): use stdpath cache for my_on_attach.lua

* fix(#2157): my_on_attach.lua -> nvim-tree-on-attach.lua

lua/nvim-tree/keymap-legacy.lua

@@ -2,6 +2,7 @@ local api = require "nvim-tree.api"
 local open_file = require "nvim-tree.actions.node.open-file"
 local keymap = require "nvim-tree.keymap"
 local notify = require "nvim-tree.notify"
+local utils = require "nvim-tree.utils"
 
 local M = {
   -- only populated when legacy mappings active
@@ -401,7 +402,7 @@ function M.cmd_generate_on_attach()
     return
   end
 
-  local name = "/tmp/my_on_attach.lua"
+  local name = utils.path_join { vim.fn.stdpath "cache", "nvim-tree-on-attach.lua" }
   local file = io.output(name)
   io.write(M.on_attach_lua)
   io.close(file)