message: Update find-the-pivot-integer.cpp
diff: class Solution {
  public:
  int pivotInteger(int n) {
  - int x = sqrt((n + 1) * n / 2);
  + int x = sqrt((n + 1) * n / 2) + 0.5;
  return x * x == (n + 1) * n / 2 ? x : -1;
  }
  };
  