minor symfony#12548 Update templates.rst (joelindix)

This PR was merged into the 4.3 branch.

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Update templates.rst

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In the last example of  'Template Inheritance and Layouts' the content block is defined in`blog/layout.html.twig`, not `blog/index.html.twig`

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7ce0f32 Update templates.rst

Author: javiereguiluz

templates.rst

@@ -893,7 +893,7 @@ template, such as ``blog/index.html.twig``, which displays the blog index:
 
 This template extends from the second-level template (``blog/layout.html.twig``)
 but overrides blocks of different parent templates: ``content`` from
-``blog/index.html.twig`` and ``title`` from ``base.html.twig``.
+``blog/layout.html.twig`` and ``title`` from ``base.html.twig``.
 
 When you render the ``blog/index.html.twig`` template, Symfony uses three
 different templates to create the final contents. This inheritance mechanism