input: Write a python function to sort a list of strings by their length.
  assert sort_string_list(['Python', 'JS', 'C++', 'Java', 'PHP']) == ['JS', 'C++', 'PHP', 'Java', 'Python']
  assert sort_string_list(['short', 'tiny', 'lengthy', 'medium']) == ['tiny', 'short', 'medium', 'lengthy']
  assert sort_string_list(['one', 'two', 'three', 'four', 'five']) == ['one', 'two', 'four', 'five', 'three']
output: def sort_string_list(strings):
      return sorted(strings, key=len)