You are given a class similar to the TicTacToe board in Section 7.6, but the board can have more than 3 rows and columns.

Your task is to complete a method that fills the four borders (that is, all cells at the left, right, top, and bottom boundary) with asterisks, like this:

********
*      *
*      *
*      *
*      *
*      *
*      *
********