implémentation de la méthode clear

Grid.java

@@ -149,6 +149,10 @@ public class Grid implements Iterable<Cell> {
      * Sets all {@link Cell}s in this {@code Grid} as dead.
      */
     void clear() {
+        GridIterator iterator = new GridIterator(this);
+        while (iterator.hasNext()) {
+            iterator.next().setDead();
+        }
     }
 
     /**