[Cache] Fix "Marshalling (Serializing) Data" code rendering issue

Author: Kocal

components/cache.rst

@@ -209,7 +209,7 @@ the cache items before storing them.
 
 The :class:`Symfony\\Component\\Cache\\Marshaller\\DefaultMarshaller` uses PHP's
 ``serialize()`` function by default, but you can optionally use the ``igbinary_serialize()``
-function from the `Igbinary extension`_:
+function from the `Igbinary extension`_::
 
     use Symfony\Component\Cache\Adapter\RedisAdapter;
     use Symfony\Component\Cache\DefaultMarshaller;