input: Write a python function to replace vowels in a string with their ASCII values.
  assert replace_vowels("Hello World") == "H101ll111 W111rld"
  assert replace_vowels("aeiou") == "9799105115117"
  assert replace_vowels("Python") == "Pyth111n"
output: def replace_vowels(s):
      vowels = "aeiouAEIOU"
      result = ""
      for char in s:
          if char in vowels:
              result += str(ord(char))
          else:
              result += char
      return result