Specification:
We want to realize a static public method that takes as parameters two positive integers x and y and computes and returns their greatest common divisor gcd(x, y).
The greatest common divisor of two integers x and y is the greatest integer that divides both x and y without rest.
Example:
| gcd(12, 8) | = | 4 |
| gcd(12, 6) | = | 6 |
| gcd(12, 7) | = | 1 |