function skewness( k ) {
	if ( isnan( k ) || k <= 0.0 ) {
		return NaN;
	}
	return sqrt( 8.0 / k );
}
Returns the skewness of a chi-squared distribution.

@param {PositiveNumber} k - degrees of freedom
@returns {PositiveNumber} skewness

@example
var v = skewness( 9.0 );
// returns ~0.943

@example
var v = skewness( 1.0 );
// returns ~2.828

@example
var v = skewness( -0.2 );
// returns NaN

@example
var v = skewness( NaN );
// returns NaN