fix 9.40

`svec.resize(svec.size()+svec.size()/2);`
if read 1000 words,`svec.resize(1500)`,capacity is 1500
Check the question: 
>If the program in the **previous exercise reads 256 words**, what is its likely capacity after it is resized.

Thus, we should write codes according to previous exercise : 
```cpp
vector<string> svec;
 svec.reserve(1024);     // sets capacity to at least 1024
 string word;
 while (cin >> word)     // input word continually
         svec.push_back(word);
 svec.resize(svec.size()+svec.size()/2); // sets capacity to at least 3/2's size. may do nothing.
```



my test codes:
```cpp
#include <iostream>
#include <vector>

using std::vector; using std::string; using std::cout; using std::endl;

void readwords(int numOfWords)
{
    vector<string> svec;
    svec.reserve(1024); // sets capacity to at least 1024
    string word{"test"};
    for (int i=0; i<numOfWords; ++i)    // input word continually
        svec.push_back(word);
    svec.resize(svec.size()+svec.size()/2); // sets capacity to at least 3/2's size. may do nothing.
    cout << "|" << numOfWords << " | " << svec.size()<< " | " << svec.capacity() << " | " << endl;
}

int main()
{
    cout << "| read | size | capacity |" << endl;
    cout << "| ---- | ---- | -------- |" << endl;
    readwords(256);
    readwords(512);
    readwords(1000);
    readwords(1048);
}
```

Output : 

| read | size | capacity |
| ---- | ---- | -------- |
|256 | 384 | 1024 |
|512 | 768 | 1024 |
|1000 | 1500 | 2000 |
|1048 | 1572 | 2048 |