turn long-term history graph into a lineplot, easier to view

The linear regression stuff makes zero sense in the long term anyways.

howto/upgrades/Makefile

@@ -2,7 +2,7 @@
 PROG=predict-os
 
 data.png: data.csv
-	$(PROG) graph -o $@ --path $<
+	$(PROG) graph -o $@ --path $< --plot-type lineplot
 
 # order of requisites matter here, the releases must be in
 # chronological order, otherwise the resulting data.csv file will be

howto/upgrades/data.csv

@@ -120,3 +120,12 @@ Date,release,count
 2024-05-07,bookworm,74
 2024-05-07,bullseye,12
 2024-05-07,buster,2
+2024-06-10,bookworm,75
+2024-06-10,bullseye,12
+2024-06-10,buster,2
+2024-09-09,bookworm,76
+2024-09-09,bullseye,12
+2024-09-09,buster,2
+2024-10-15,bookworm,77
+2024-10-15,bullseye,12
+2024-10-15,buster,1