minor symfony#8021 Added a missing <script> tag in an example (javiereguiluz)

This PR was squashed before being merged into the 2.7 branch (closes symfony#8021).

Discussion
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Added a missing <script> tag in an example

It's obvious that this code is JavaScript ... but to make it consistent with the other example of the article, I propose to add the `<script>` tags to the second example. Close it if you disagree. Thanks!

Commits
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2323e19 Added a missing <script> tag in an example

Author: xabbuh

routing/generate_url_javascript.rst

@@ -26,10 +26,12 @@ variables. The ``escape()`` function helps escape any non-JavaScript-safe values
 But if you *actually* need to generate routes in pure JavaScript, consider using
 the `FOSJsRoutingBundle`_. It makes the following possible:
 
-.. code-block:: javascript
+.. code-block:: html+twig
 
+    <script>
     var url = Routing.generate('blog_show', {
         'slug': 'my-blog-post'
     });
+    </script>
 
 .. _`FOSJsRoutingBundle`: https://github.com/FriendsOfSymfony/FOSJsRoutingBundle