Create a function that takes an array of numbers and returns the greatest common factor of those numbers.
gcd({84, 70, 42, 56}) ➞ 14
gcd({19, 38, 76, 133}) ➞ 19
gcd({120, 300, 95, 425, 625}) ➞ 5The GCD is the largest factor that divides all numbers in the array.