[DependencyInjection] fixed espacing issue (close #2819)

src/Symfony/Component/DependencyInjection/Dumper/XmlDumper.php

@@ -145,7 +145,8 @@ class XmlDumper extends Dumper
         }
 
         if ($definition->getFile()) {
-            $file = $this->document->createElement('file', $definition->getFile());
+            $file = $this->document->createElement('file');
+            $file->appendChild($this->document->createTextNode($definition->getFile()));
             $service->appendChild($file);
         }