message: Update check for VS2015
diff: namespace fs
  {
  -#if defined(_WIN32) || defined(__cpp_lib_filesystem)
  +// VS2015 (_MSC_VER 1900) uses std::experimental::filesystem
  +#if (defined(_MSC_VER) && _MSC_VER > 1900) || defined(__cpp_lib_filesystem)
  namespace stdfs = std::filesystem;
  #else
  namespace stdfs = std::experimental::filesystem;
  