[BUG] Sparkline issue when series max and min are the same

[FrancisMurilloDigix]

Hi.

Thanks for this library, was able to create a small monitoring tool for my requirement. Just want to report on a possible bug where a Sparkline series has the same min and max value possibly causing an arithmetic error. The snippet below has this error:

panel title: "LINES:" do
  sparkline(series: [1])     # Error
  sparkline(series: [1,1])  # Error
  sparkline(series: [1,2])  # Works
end

I noticed in Ratatouille.Renderer.Element.Sparkline.normalize has this possibility:

defp normalize({min, max}, value) do
  x = (value - min) / (max - min)
  round(x * @range)
end

Not sure if this is intended or is better handled by another component. Thanks again.