Update front-page examples

_includes/frontpage_javascript_example1.md

@@ -1,7 +1,7 @@
 ```javascript
 actor {
-  this.balance = 0;
   react {
+    field this.balance = 0;
     assert account(this.balance);
     on message deposit($amount) {
       this.balance += amount;

_includes/frontpage_racket_example1.md

@@ -1,7 +1,7 @@
 ```racket
 (actor
- (forever #:collect [(balance 0)]
-   (assert (account balance))
-   (on (message (deposit $amount))
-       (+ balance amount))))
+ (react (field [balance 0])
+        (assert (account (balance)))
+        (on (message (deposit $amount))
+            (balance (+ (balance) amount)))))
 ```

_includes/frontpage_racket_example2.md

@@ -1,7 +1,6 @@
 ```racket
 (actor
- (forever
-   (on (asserted (account $balance))
-       (printf "Balance: ~a\n"
-               balance))))
+ (react (on (asserted (account $balance))
+            (printf "Balance: ~a\n"
+                    balance))))
 ```