sortBy() fails to sort this table of values

[drauschenbach]

$ lua
Lua 5.2.4  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> _=require 'lodash'
> inspect=require 'inspect'
> print(inspect(_.sortBy{16, 12, 20, 13, 17, 14, 18, 10, 19, 15, 11}))

{ 12, 16, 13, 17, 14, 18, 10, 19, 15, 11, 20 }