mod_auth_token: Timezone fix for TOTP checking luatz.time() returns milliseconds since epoch which is in UTC time, so we don't need to convert to UTC with gmtime. By calling gmtime, TOTP validation was failing when this module wasn't running on machine set to UTC time.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.