GPG signatures missing for versions 1.8.5 and 1.8.6

This is a follow up to the following issues:
https://github.com/arduino/ArduinoCore-avr/issues/458
https://github.com/arduino/ArduinoCore-avr/issues/518

I'll immediately close my issue after this one is created and if the signatures are in place, #458 can be closed also.

The current packaging process for Arch Linux requires a GPG signature to exist. The following signatures are missing:
https://downloads.arduino.cc/cores/staging/avr-1.8.5.tar.bz2.asc
https://downloads.arduino.cc/cores/staging/avr-1.8.6.tar.bz2.asc

Would be great if someone could sign these packages and upload the signature files.

Review linked issues #458 and #518, then check whether avr-1.8.5.tar.bz2.asc and avr-1.8.6.tar.bz2.asc exist at the staging download URLs. Done means both package signature files have been generated, uploaded, and are available for the Arch Linux packaging process.

Written by the indexing model from the issue text.