hotfix function name in tictactoe

lessons/beginners-en/tictactoe/index.md

@@ -67,10 +67,12 @@ def pc_move(board):
 
 ## Step 5
 
-Write a `1D_tictactoe` function that creates a string with a game board and alternately calls the `player_move` and
+Write a `tictactoe_1d` function that creates a string with a game board and alternately calls the `player_move` and
 `pc_move` functions until someone wins or draws.
 Do not forget to check the status of the game after every turn.
 
+Hint: Defining a function with a name starting with a number is not possible. That is why we do not use function name `1d_tictactoe`. 
+
 ## Step 6 - Optional
 Can you think of better strategy for your computer? 
 Let us know your ideas or try to program them directly.