input: Write a python function to generate a random password of a given length using lowercase letters.
  assert len(randomString(10)) == 10
  assert len(randomString(15)) == 15
  assert all(c in string.ascii_lowercase for c in randomString(20))
output: import random
  import string
  
  def randomString(length):
      return ''.join(random.choices(string.ascii_lowercase, k=length))