fix subject of rust/tic_tac_toe

subjects/tic_tac_toe/README.md

@@ -11,7 +11,7 @@ Create the following functions:
     - It should return a String `player O won` or `player X won` or `Tie`.
 - `diagonals` which will receive:
     - a player and a table. 
-    - It should return a boolean, this must return `true` if all the diagonals are completed by the player.
+    - It should return a boolean, this must return `true` if one of the diagonals are completed by the player.
 - `horizontal` which will receive:
     - a player and a table. 
     - It should return a boolean, this must return `true` if one of the horizontal lines are completed by the player.