function getContrast(color1, color2) {
    var luminance1 = getLuminance(color1);
    var luminance2 = getLuminance(color2);
    return parseFloat((luminance1 > luminance2 ? (luminance1 + 0.05) / (luminance2 + 0.05) : (luminance2 + 0.05) / (luminance1 + 0.05)).toFixed(2));
  }
Returns the contrast ratio between two colors based on
[W3's recommended equation for calculating contrast](http://www.w3.org/TR/WCAG20/#contrast-ratiodef).

@example
const contrastRatio = getContrast('#444', '#fff');