net-im/gajim: update to 1.3.1

https://gajim.org/post/2021-02-08-gajim-1.3.0-released/
https://gajim.org/post/2021-03-01-gajim-1.3.1-released/

Thank you Goran Mekić for help with testing!

PR: 248559
Submitted by: yzrh@noema.org (based on)
Tested by: Goran Mekić <meka@tilda.center>