[TwigBundle] activated Twig Optimizer extension by default

src/Symfony/Bundle/TwigBundle/Resources/config/twig.xml

@@ -38,6 +38,10 @@
             <tag name="twig.extension" />
         </service>
 
+        <service id="twig.extension.optimizer" class="Twig_Extension_Optimizer">
+            <tag name="twig.extension" />
+        </service>
+
         <service id="twig.extension.trans" class="Symfony\Bundle\TwigBundle\Extension\TransExtension">
             <tag name="twig.extension" />
             <argument type="service" id="translator" />