Update transposition snippet (python)

zip is a nice trick but it doesn't output a matrix. The output of zip is an iterator of tuples. You can't use it for accessing elements of matrix by index.

`transposed_matrix[0][0]` will raise an error
`TypeError: 'zip' object is not subscriptable`

apps/website/contents/algorithms/matrix.md

@@ -59,7 +59,7 @@ Many grid-based games can be modeled as a matrix, such as Tic-Tac-Toe, Sudoku, C
 Transposing a matrix in Python is simply:
 
 ```py
-transposed_matrix = zip(*matrix)
+transposed_matrix = [[matrix[i][j] for i in range(len(matrix))] for j in range(len(matrix[0]))]
 ```
 
 ## Essential questions