input: Write a function to print the Fibonacci series up to n numbers where n is a user input.
  assert fibonacci_series(10)==[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
  assert fibonacci_series(5)==[0, 1, 1, 2, 3]
  assert fibonacci_series(1)==[0]
output: def fibonacci_series(n):
      if n == 1:
          return [0]
      elif n == 2:
          return [0, 1]
      else:
          fib_series = [0, 1]
          for i in range(2, n):
              fib_series.append(fib_series[-1] + fib_series[-2])
          return fib_series