AOSA-2016-0017: update Irssi to 0.8.20

Please update your irssi package to version 0.8.20.

Irssi has announced a security advisory describing that the following security vulnerabilities were fixed with the newly released Irssi 0.8.20:

CVE-2016-7044, CVE-2016-7045, CVE-2016-7553 (reserved but not issued).

Relevant documentation:

• Heap corruption and missing boundary checks.