input: Write a python function to find the first odd number in a list.
  assert first_odd([1, 4, 5, 6, 9, 10, 11])==1
  assert first_odd([2, 4, 6, 8, 10, 12, 15])==15
  assert first_odd([2, 4, 6, 8, 10, 12, 14])==None
output: def first_odd(numbers):
      for number in numbers:
          if number % 2 != 0:
              return number
      return None