Given a string `s` and an integer `k`, return the maximum number of vowel letters in any substring of `s` with length `k`.

Vowel letters in English are `'a'`, `'e'`, `'i'`, `'o'`, and `'u'`.

Example 1:

    Input: s = "abciiidef", k = 3
    Output: 3
    Explanation: The substring "iii" contains 3 vowel letters.

Example 2:

    Input: s = "aeiou", k = 2
    Output: 2
    Explanation: Any substring of length 2 contains 2 vowels.

Example 3:

    Input: s = "leetcode", k = 3
    Output: 2
    Explanation: "lee", "eet" and "ode" contain 2 vowels.

Constraints:

- `1 <= s.length <= 105`
- `s` consists of lowercase English letters.
- `1 <= k <= s.length`