Negative value in viewBox attribute

[Postnov]

When files are compiled, negative values become positive and "NaN" is added before them. NaN is not a problem, I remove it with gulp-replace. The problem is that I cannot return negative viewBox values, which gulp-svg-sprites replaced with positive ones.

Gulp-task

.pipe(svgSprite({
    mode: "symbols",
    // preview: false,
    selector: "svg-%f",
    svg: {
        symbols: 'svg_sprite.pug'
    }
}

Init svg viewBox: viewBox="-49 141 512 512"
Finish svg viewBox: viewBox="NaN 49 141 512 512"