[DoctrineBundle] resolve parameters inside DATABASE_URL

Author: nicolas-grekas

doctrine/doctrine-bundle/1.6/config/packages/doctrine.yaml

@@ -1,6 +1,7 @@
 doctrine:
     dbal:
-        url: '%env(DATABASE_URL)%'
+        # With Symfony 3.3, remove the `resolve:` prefix
+        url: '%env(resolve:DATABASE_URL)%'
     orm:
         auto_generate_proxy_classes: '%kernel.debug%'
         naming_strategy: doctrine.orm.naming_strategy.underscore