BIP39: fix word in Italian wordlist special considerations

Corrected terminology: "double vocals" → "double vowels" ### Explanation of Change: 1. The rule being described refers to spelling and letter patterns, specifically when two vowel letters appear together. 2. The term "vowels" is the proper linguistic term for such letters, while "vocals" is incorrect in this context. 3. The example "lineetta" demonstrates a double vowel pattern ('ee').

Specification