input: Write a python function to find the most common element in a list.
  assert mostCommonElement([1, 2, 3, 1, 2, 1]) == 1
  assert mostCommonElement(['a', 'b', 'a', 'c', 'a', 'b', 'b']) == 'a'
  assert mostCommonElement([10, 20, 20, 30, 30, 30]) == 30
output: def mostCommonElement(lst):
      from collections import Counter
      count = Counter(lst)
      return count.most_common(1)[0][0]