Logarithmic Zooming with mousewheel not centered

[amosmatter]

When Zooming with the mouswheel, the Zoom center is not where the mouse is if the scale is logarithmic. To fix this, the values would need to be mapped to a logarithmic scale before applying zoomdelta and back to exponential after. I created a small workaround which seems to work in my usecase:

    zoomPlugin.zoomFunctions.logarithmic = (scale, zoom, center, limits) => {
    const {id, axis, options: scaleOpts} = scale;

    const centerPoint = scale.isHorizontal() ? center.x : center.y;

    const val = scale.getValueForPixel(centerPoint)
    if (val === undefined) {
      return true;
    }

    const logmin = Math.log10(scale.min);
    const logmax = Math.log10(scale.max);
    const logval = Math.log10(val);

    const range = logmax - logmin;
    const zoomRange = range * (zoom - 1);

    const minPercent = Math.max(0, Math.min(1, (logval - logmin) / range || 0));
    const maxPercent = 1 - minPercent;

    const newlogmin = minPercent * zoomRange;
    const newlogmax = maxPercent * zoomRange;

    scaleOpts.min = Math.pow(10, logmin + newlogmin);
    scaleOpts.max = Math.pow(10, logmax - newlogmax);
    return false;
    };

[kurkle]

Would you be willing to make a pull request for this?