input: Write a python function to perform a linear search on a list.
  assert linearSearch([5, 3, 7, 2], 7) == 2
  assert linearSearch([10, 20, 30, 40, 50], 30) == 2
  assert linearSearch([1, 2, 3, 4, 5], 6) == -1
output: def linearSearch(lst, target):
      for i in range(len(lst)):
          if lst[i] == target:
              return i
      return -1