PerpSlope = function (line)
{
    return -((line.x2 - line.x1) / (line.y2 - line.y1));
}
Calculate the perpendicular slope of the given line.

@function Phaser.Geom.Line.PerpSlope
@since 3.0.0

@param {Phaser.Geom.Line} line - The line to calculate the perpendicular slope of.

@return {number} The perpendicular slope of the line.