[solution 18.3] Fix counting live cells around right/bottom of board

Issue marijnh#165

Author: marijnh

code/solutions/18_3_conways_game_of_life.html

@@ -42,10 +42,10 @@
   // center field.
   function countNeighbors(grid, x, y) {
     var count = 0;
-    for (var y1 = Math.max(0, y - 1); y1 <= Math.min(height, y + 1); y1++) {
-      for (var x1 = Math.max(0, x - 1); x1 <= Math.min(width, x + 1); x1++) {
+    for (var y1 = Math.max(0, y - 1); y1 <= Math.min(height - 1, y + 1); y1++) {
+      for (var x1 = Math.max(0, x - 1); x1 <= Math.min(width - 1, x + 1); x1++) {
         if ((x1 != x || y1 != y) && grid[x1 + y1 * width])
-          count +=1 ;
+          count += 1;
       }
     }
     return count;