Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an integer array nums, return the greatest common divisor of the smallest number and largest number in nums.
The greatest common divisor of two numbers is the largest positive integer that evenly divides both numbers.
 
Please complete the following python code precisely:
```python
class Solution:
    def findGCD(self, nums: List[int]) -> int:
```