Example code in Scanner class

There is one using `System.in` as:
```
     Scanner sc = new Scanner(System.in);
```
With JEP 400, the default charset and console charset may differ, thus this example may result in an unexpected one if the user tries to read a String from the scanner. This should be replaced with:
```
    Scanner sc = new Scanner(Console.reader())
```
so that the user would not have to take encoding into consideration.