Fix maximum y-value-range computation
Summary:
Rounding to the next 10 did not work if the maximum value was something like y_max = 30.947
In this case modulo 10 gives 0 and therefore the maximum values becomes 30 in the end, though it should be 40
otherwise the peak points outside of the chart.
Floor(max) + 10 always works.
Test Plan:
Before:
After:
Reviewers: VDG, Plasma, ngraham
Reviewed By: VDG, ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D24029