For anyone interested in the changes i made to the graphs, you can download the two relevant files from github instead of editing them with the commands below.
(Changes: Fix data collection of Messages >-3dB and display those messages better)
On the raspberry pi execute the following commands and be sure to copy the entire lines:
cd /home/pi/adsb-receiver/build/portal/graphs
wget https://raw.githubusercontent.com/wiedehopf/adsb-receiver/freeze/build/portal/graphs/make-collectd-graphs.sh -O make-collectd-graphs.sh
wget https://raw.githubusercontent.com/wiedehopf/adsb-receiver/freeze/build/portal/graphs/dump1090.py -O dump1090.py
sudo systemctl restart collectd
Enjoy improved graphs.
Restoring the original files:
cd /home/pi/adsb-receiver/build/portal/graphs
git checkout dump1090.py make-collectd-graphs.sh
sudo systemctl restart collectd
Edit: Changed the graph slightly to improve spacing between the number and the percent sign.