fix(updater): format Update.date to RFC 3339 (#2573)

* fix(updater): format `Update.date` to RFC 3339

* Messed up on argument in #2572

* Format

* Update example

* Avoid extra to_string

* Deprecate `Update.available`

examples/api/src/views/Updater.svelte

@@ -12,10 +12,14 @@
     isChecking = true
     try {
       const update = await check()
-      onMessage(`Should update: ${update.available}`)
-      onMessage(update)
+      if (update) {
+        onMessage(`Should update: ${update.available}`)
+        onMessage(update)
 
-      newUpdate = update
+        newUpdate = update
+      } else {
+        onMessage('No update available')
+      }
     } catch (e) {
       onMessage(e)
     } finally {