input: Write a function to find the most common element in a list.
  assert most_common_element([3, 4, 2, 3, 5, 3, 2, 3]) == 3
  assert most_common_element([1, 1, 2, 2, 2, 3, 3, 3]) == 2
  assert most_common_element([10, 20, 10, 20, 30, 10, 40, 50]) == 10
output: def most_common_element(lst):
      from collections import Counter
      count = Counter(lst)
      return count.most_common(1)[0][0]