[mythtvnz] My upgrade to 31.0

[Robert Fisher]

I just painlessly upgraded MythTV on Ubuntu 18.04 from 30 to 31 as follows:-

( found the last upgrade painless too so I didn't even bother to backup 
the database)

sudo add-apt-repository ppa:mythbuntu/31
sudo apt update
sudo apt dist-upgrade
sudo shutdown -r now
sudo add-apt-repository -r ppa:mythbuntu/30