input: Write a function to perform linear search on a list.
  assert linearSearch([1, 2, 3, 4, 5], 3) == 2
  assert linearSearch([10, 20, 30, 40, 50], 40) == 3
  assert linearSearch([5, 10, 15, 20, 25], 7) == -1
output: def linearSearch(lst, target):
      for index, value in enumerate(lst):
          if value == target:
              return index
      return -1