Update net-im/qxmpp-qt5 to latest upstream release

Release notes at
https://github.com/qxmpp-project/qxmpp/releases/tag/v1.3.1

The most important change of this release is the fix of CVE-2017-5603.
QXmpp is not vulnerable to roster push attacks (CVE-2016-9928).

Reported by: portscout
MFH: 2020Q3