Updated preferred username comment in MSALAccount
Updated preferred username comment in MSALAccount

AzureAD/microsoft-authentication-library-for-objc,AzureAD/microsoft-authentication-library-for-objc,AzureAD/microsoft-authentication-library-for-objc,AzureAD/microsoft-authentication-library-for-objc,AzureAD/microsoft-authentication-library-for-objc