Diplay the day of the week on chart x-axis labels#147

It’s nice to know at a glance that, for example, “14 June” was a Sunday. So when I see a dip in traffic I can quickly realize that everyone was AFK and it’s nothing to be worried about. 😎

Thank you for your contribution. We’re moving this thread to Github: https://github.com/plausible/analytics/issues/175