docs(template-syntax): typo

closes #627

public/docs/ts/latest/guide/template-syntax.jade

@@ -578,7 +578,7 @@ code-example(format="", language="html").
   Now imagine a parent component that listens for that event with an Event Binding.
 +makeExample('template-syntax/ts/app/app.component.html', 'event-binding-to-component')(format=".")
 :marked
-  The event binding surfaces the *hero-to-delete* emitted by `HeroDetail` to the expression via the `$hero` variable.
+  The event binding surfaces the *hero-to-delete* emitted by `HeroDetail` to the expression via the `$event` variable.
   We pass it along to the parent `onHeroDeleted()` method.
   That method presumably knows how to delete the hero.