input: Write a python function to find the most common element in a list.
  assert findCommonElement([8, 5, 5, 9, 8, 6, 5]) == 5
  assert findCommonElement([1, 2, 2, 3, 4, 4, 4, 5]) == 4
  assert findCommonElement([7, 8, 8, 7, 7, 9, 9, 9, 9]) == 9
output: def findCommonElement(lst):
      from collections import Counter
      return Counter(lst).most_common(1)[0][0]