[doctrine-bundle] add single quotes for DATABASE_URL

doctrine/doctrine-bundle/1.6/manifest.json

@@ -10,6 +10,6 @@
         "#1": "Format described at http://docs.doctrine-project.org/projects/doctrine-dbal/en/latest/reference/configuration.html#connecting-using-a-url",
         "#2": "For an SQLite database, use: \"sqlite:///%kernel.project_dir%/var/data.db\"",
         "#3": "Configure your db driver and server_version in config/packages/doctrine.yaml",
-        "DATABASE_URL": "mysql://db_user:db_password@127.0.0.1:3306/db_name"
+        "DATABASE_URL": "'mysql://db_user:db_password@127.0.0.1:3306/db_name'"
     }
 }