Merge branch '3.4' into 4.3

* 3.4:
  fix wrong class import
  Fix the chain adapter exemple on object creation

Author: OskarStark

components/cache/adapters/chain_adapter.rst

@@ -15,16 +15,15 @@ given adapters. This exposes a simple and efficient method for creating a layere
 The ChainAdapter must be provided an array of adapters and optionally a maximum cache
 lifetime as its constructor arguments::
 
-    use Symfony\Component\Cache\Adapter\ApcuAdapter;
-
-    $cache = new ChainAdapter([
+    use Symfony\Component\Cache\Adapter\ChainAdapter;
 
+    $cache = new ChainAdapter(
         // The ordered list of adapters used to fetch cached items
         array $adapters,
 
         // The max lifetime of items propagated from lower adapters to upper ones
         $maxLifetime = 0
-    ]);
+    );
 
 .. note::