[DoctrineBundle] fixed invalid parameter error

src/Symfony/Bundle/DoctrineBundle/DependencyInjection/DoctrineExtension.php

@@ -226,7 +226,7 @@ class DoctrineExtension extends AbstractDoctrineExtension
             if (false === @mkdir($proxyCacheDir, 0777, true)) {
                 throw new \RuntimeException(sprintf('Unable to create the Doctrine Proxy directory (%s)', dirname($proxyCacheDir)));
             }
-        } elseif (!is_writable($proxyCacheDir) && $container->getParameter('auto_generate_proxy_classes') == true) {
+        } elseif (!is_writable($proxyCacheDir) && $container->getParameter('doctrine.orm.auto_generate_proxy_classes') == true) {
             throw new \RuntimeException(sprintf('Unable to write in the Doctrine Proxy directory (%s)', $proxyCacheDir));
         }
     }