Fix $el example

Use the same wording as in the demo

packages/docs/src/en/magics/el.md

@@ -9,7 +9,7 @@ title: el
 `$el` is a magic property that can be used to retrieve the current DOM node.
 
 ```html
-<button @click="$el.innerHTML = 'foo'">Replace me with "foo"</button>
+<button @click="$el.innerHTML = 'Hello World!'">Replace me with "Hello World!"</button>
 ```
 
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