Fix JS syntax on Action Cable Overview

Change two JavaScript examples in the Action Cable Overview guide to fix
a couple of issues that seem to come from employing rubyisms:

- a syntax error by using keyword arguments instead of a plain object
- using == instead of === - this should be avoided if at all possible

Author: coiti

guides/source/action_cable_overview.md

@@ -585,7 +585,7 @@ consumer.subscriptions.create("AppearanceChannel", {
   },
 
   get documentIsActive() {
-    return document.visibilityState == "visible" && document.hasFocus()
+    return document.visibilityState === "visible" && document.hasFocus()
   },
 
   get appearingOn() {
@@ -653,7 +653,7 @@ import consumer from "./consumer"
 
 consumer.subscriptions.create("WebNotificationsChannel", {
   received(data) {
-    new Notification(data["title"], body: data["body"])
+    new Notification(data["title"], { body: data["body"] })
   }
 })
 ```