In `5-UsefulConceptsAndSTL/7-Algorithms.ipynb#std::unique` some values should be erased

std::vector::erase() may be introduced before, in section 5-UsefulConceptsAndSTL/7-Algorithms.ipynb#std::unique as the result is not correct at the end of:

#include <vector>
#include <algorithm>
#include <iostream>

{
    std::vector<int> int_vec { -9, 87, 11, 0, -21, 100, -21, 17, -21 }; 
   
    std::sort(int_vec.begin(), int_vec.end());
    std::unique(int_vec.begin(), int_vec.end());
       
    std::cout << "The unique values are (really this time): ";
    
    for (auto item : int_vec)
        std::cout << item << " ";
    
    std::cout << std::endl;
}
// The unique values are (really this time): -21 -9 0 11 17 87 100 87 100 

The last 87 100 is not what we want.