input: Write a function to find the shortest string in a list.
  assert find_shortest(["apple", "banana", "cherry", "date"]) == "date"
  assert find_shortest(["elephant", "dog", "cat", "hippopotamus"]) == "cat"
  assert find_shortest(["one", "two", "three", "four"]) == "one"
output: def find_shortest(strings):
      return min(strings, key=len)