Don't round charted data to the closest integer

It seems that all values I can get the graph to show are rounded to integers. That makes sense for all of them, except for values per 100k/1M people. The quantization of those causes logscale per-population graphs to look very staircasey, see e.g. https://rys.io/covid/#delta,per100k,date;poland,switzerland

(original report on fedi)