message: Update letter-case-permutation.cpp
diff: @@ -10,8 +10,8 @@ public:
  const auto& size = result.size();
  for (int i = 0; i < size; ++i) {
  result.emplace_back(result[i]);
  - result.back() += toupper(c);
  result[i] += tolower(c);
  + result.back() += toupper(c);
  }
  } else {
  for (auto &s : result) {
  