erlang: bump to version 18.2.1

This is a major release of Erlang that includes a licensing change from
the EPL to the Apache License, significant changes to the timer APIs, better
support for large maps, and security improvements.

Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>