This is not a severe problem. It simply says that the file in
/etc/apt/apt.conf.d/20auto-upgrades.ucf-dist is ignored because of invalid file extension. Remove the extension and it should be all OK.
sudo mv /etc/apt/apt.conf.d/20auto-upgrades.ucf-dist /etc/apt/apt.conf.d/20auto-upgrades
is the command you'll run to rename it.
In my 16.04, the content of the file is some configuration options related to
apt that control whether or not automatic package update will run and automatic cleaning of packages will occur. Here is the content of it