input: Write a function to generate the Fibonacci sequence up to the n-th element.
  assert fibonacci(5) == [0, 1, 1, 2, 3, 5]
  assert fibonacci(7) == [0, 1, 1, 2, 3, 5, 8, 13]
  assert fibonacci(10) == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
output: def fibonacci(n):
      sequence = [0, 1]
      for i in range(2, n + 1):
          sequence.append(sequence[-1] + sequence[-2])
      return sequence[:n + 1]