Fix namespace/filepath mismatch found by DOCtor-RST

- Fix FooExtractor filepath from src/Acme/DemoBundle/Translation to src/DemoBundle/Translation

Author: OskarStark

reference/dic_tags.rst

@@ -1101,7 +1101,7 @@ You can create your own extractor by creating a class that implements
 and tagging the service with ``translation.extractor``. The tag has one
 required option: ``alias``, which defines the name of the extractor::
 
-    // src/Acme/DemoBundle/Translation/FooExtractor.php
+    // src/DemoBundle/Translation/FooExtractor.php
     namespace Acme\DemoBundle\Translation;
 
     use Symfony\Component\Translation\Extractor\ExtractorInterface;