rkhunter and unattended-upgrades

I have an Ubuntu 18.04 system running with rkhunter installed. I keep getting warnings in the rkhunter.log after unattended-upgrades has upgraded the system. The solution to this would be running rkhunter --propupd after every automatic upgrade. [I found this](https://help.ubuntu.com/community/RKhunter) which mentions /etc/apt/apt.conf.d/90rkhunter, however, this file doesn't exist on my system. How can I make sure rkhunter --propupd is being executed after unattended-upgrades are done?