function kurtosis( a, b ) {
	if (
		isnan( a ) ||
		isnan( b ) ||
		a >= b
	) {
		return NaN;
	}
	return -1.2;
}
Returns the excess kurtosis of a uniform distribution.

@param {number} a - minimum support
@param {number} b - maximum support
@returns {number} excess kurtosis

@example
var v = kurtosis( 0.0, 1.0 );
// returns -1.2

@example
var v = kurtosis( 4.0, 12.0 );
// returns -1.2

@example
var v = kurtosis( -4.0, 4.0 );
// returns -1.2

@example
var v = kurtosis( 1.0, -0.1 );
// returns NaN

@example
var v = kurtosis( 2.0, NaN );
// returns NaN

@example
var v = kurtosis( NaN, 2.0 );
// returns NaN