message: Update roman-to-integer.cpp
  add one extra condition even the leetcode didn't care about it
diff: @@ -8,7 +8,7 @@ public:
  {'L', 50}, {'C', 100}, {'D', 500},
  {'M', 1000}};
  return accumulate(s.crbegin() , s.crend() , 0 , [&numeral_map](int sum , char c){
  - return sum += ((numeral_map[c] * 5 <= sum) ? -numeral_map[c]: numeral_map[c]);
  + return sum += ((numeral_map[c] * 5 <= sum) && (c!= 'M') ? -numeral_map[c]: numeral_map[c]);
  });
  }
  };
  