Update crowdsec-firewall-bouncer to latest upstream release version 0.0.21

Makefile rework
- use tagged version for download

Fixes
- set API_KEY in firewall bouncer config file

Signed-off-by: Kerma Gérald <gandalf@gk2.net>

/net/crowdsec-firewall-bouncer/

crowdsec-firewall-bouncer will fetch new and old decisions from
 a CrowdSec API to add them in a blocklist used by supported firewalls.

Signed-off-by: Kerma Gérald <gandalf@gk2.net>