fix variable name

there is no $memcache variable in this closure

Author: dominikzogg

src/Dflydev/Pimple/Provider/DoctrineOrm/DoctrineOrmServiceProvider.php

@@ -213,7 +213,7 @@ public function register(\Pimple $app)
             $memcached->addServer($cacheOptions['host'], $cacheOptions['port']);
 
             $cache = new MemcachedCache;
-            $cache->setMemcached($memcache);
+            $cache->setMemcached($memcached);
 
             return $cache;
         });