Plasma 5.6.4 available in Kubuntu 16.04 Backports

Plasma 5.6.4 Announcement:
https://www.kde.org/announcements/plasma-5.6.4.php

How to get the update:
1. sudo apt-add-repository ppa:kubuntu-ppa/backports
2. sudo apt update
3. sudo apt full-upgrade -y