[BUG] Rounding issue with log scale labels

[qoheniac]

In Plotters 0.3.7 building a chart with .build_cartesian_2d(0..100, (1e-15..1e1).log_scale()) gives me:

[qoheniac]

Here is a minimal example:

use plotters::prelude::*;
fn main() {
    let drawing_area = SVGBackend::new("example.svg", (500, 500)).into_drawing_area();
    drawing_area.fill(&WHITE).unwrap();
    let mut chart_context = ChartBuilder::on(&drawing_area)
        .set_left_and_bottom_label_area_size(30)
        .margin(10)
        .build_cartesian_2d(0..100, (1e-15..1e1).log_scale())
        .unwrap();
    chart_context.configure_mesh().draw().unwrap();
}