input: Write a python function to generate a list of first n Fibonacci numbers.
  assert fibonacci(6) == [0, 1, 1, 2, 3, 5]
  assert fibonacci(10) == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
  assert fibonacci(1) == [0]
output: def fibonacci(n):
      if n <= 0:
          return []
      elif n == 1:
          return [0]
      
      fib_list = [0, 1]
      for i in range(2, n):
          fib_list.append(fib_list[-1] + fib_list[-2])
      
      return fib_list