function mode( mu ) {
	return addon( mu );
}
Returns the mode of a degenerate distribution with constant value `mu`.

@private
@param {number} mu - constant value of the distribution
@returns {number} mode

@example
var y = mode( 0.1 );
// returns 0.1

@example
var y = mode( 4.0 );
// returns 4.0

@example
var y = mode( -4.0 );
// returns -4.0

@example
var y = mode( NaN );
// returns NaN