input: Write a python function to perform a linear search on a list.
  assert linearSearch([4, 3, 1, 7, 9, 6], 9) == 4
  assert linearSearch([4, 3, 1, 7, 9, 6], 1) == 2
  assert linearSearch([4, 3, 1, 7, 9, 6], 5) == -1
output: def linearSearch(lst, target):
      for index, value in enumerate(lst):
          if value == target:
              return index
      return -1