When I create a line chart with a custom offset like this:

Chartist.Line(Node, {labels, series}, {
  axisY: {
    offset: 0
  }
})

I'm getting this error:

I can't figure it out why this - 10 in this line is necessary, but looks like it is some hard coded value, and removing it resolves problem.

I'm presume this will cause a visual change for the apps which are currently using the lib. Anyway, I've readed the contributing file, but let me know if this PR is ok