input: Write a python function to replace zeros in a list with -1.
  assert replace_zeros([1, 0, 2, 4, 0, 5])==[1, -1, 2, 4, -1, 5]
  assert replace_zeros([0, 0, 0, 0])==[-1, -1, -1, -1]
  assert replace_zeros([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
output: def replace_zeros(lst):
      return [-1 if x == 0 else x for x in lst]