minor #5896 [Book][Templating] Update absolute URL asset to match 2.7 (lemoinem)

This PR was merged into the 2.7 branch.

Discussion
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[Book][Templating] Update absolute URL asset to match 2.7

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.7+
| Fixed tickets | N/A

As mentionned in http://symfony.com/blog/new-in-symfony-2-7-the-new-asset-component, the Right Way:tm: to generate absolute url assets is now through `absolute_url(assset(...))`...

Commits
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44c8630 [Book][Templating] Update absolute URL asset to match 2.7

Author: xabbuh

book/templating.rst

@@ -1098,7 +1098,7 @@ if you are using Twig (or the third argument if you are using PHP) to ``true``:
 
     .. code-block:: html+jinja
 
-        <img src="{{ asset('images/logo.png', absolute=true) }}" alt="Symfony!" />
+        <img src="{{ absolute_url(asset('images/logo.png')) }}" alt="Symfony!" />
 
     .. code-block:: html+php