function mgf( t, k ) {
	return addon( t, k );
}
Evaluates the moment-generating function (MGF) for a chi-squared distribution with degrees of freedom `k` at a value `t`.

@private
@param {number} t - input value
@param {NonNegativeNumber} k - degrees of freedom
@returns {number} evaluated MGF

@example
var v = mgf( 0.4, 2.0 );
// returns ~5.0

@example
var v = mgf( -1.0, 5.0 );
// returns ~0.0642

@example
var v = mgf( 0.0, 10.0 );
// returns 1.0

@example
var v = mgf( NaN, 5.0 );
// returns NaN