input: Write a function to count the number of vowels in a string using regular expressions.
  assert count_vowels("Hello World!") == 3
  assert count_vowels("Python Programming") == 4
  assert count_vowels("aeiouAEIOU") == 10
output: def count_vowels(s):
      import re
      return len(re.findall(r'[aeiouAEIOU]', s))