Vojtěch,
Upgrade to Debian 9.
We will make a back up of your sources.list file then change it to debian 9.
As root:
apt-get update && apt-get upgrade
Then as root make a backup of sources list.
cp /etc/apt/sources.list /etc/apt/sources.list.bak
Change sources list from Debian 8 to Debian 9.
sed -i 's/jessie/stretch/g' /etc/apt/sources.list
Now the sources.list has been updated.
Continue as root:
apt-get update && apt-get upgrade && apt-get dist-upgrade
That will make you Debian 9.
You will have the correct files then.
Best regards,
David