shallow_copy for upgrade test

spec/helpers/http_mock/nginx_instance.lua

@@ -14,9 +14,16 @@ local error = error
 local assert = assert
 local ngx = ngx
 local io = io
--- It can't be changed to kong.tools.table because the old version
--- does not have kong/tools/table.lua, so the upgrade test will fail.
-local shallow_copy = require("kong.tools.utils").shallow_copy
+
+local shallow_copy
+do
+  local clone = require "table.clone"
+
+  shallow_copy = function(orig)
+    assert(type(orig) == "table")
+    return clone(orig)
+  end
+end
 
 local template = assert(pl_template.compile(template_str))
 local render_env = {ipairs = ipairs, pairs = pairs, error = error, }