[composer] make doctrine dbal and orm recommended by doctrine-bridge

src/Symfony/Bridge/Doctrine/composer.json

@@ -17,7 +17,10 @@
         }
     ],
     "require": {
-        "php": ">=5.3.2",
+        "php": ">=5.3.2"
+    },
+    "recommend": {
+        "doctrine/dbal": ">=2.1",
         "doctrine/orm": ">=2.1"
     },
     "suggest": {