Revert "Fix demo PDOCollector name, and update it with 72fea42" (#595)

* Revert "Fix demo PDOCollector name, and update it with 72fea42 (#593)"

This reverts commit 43632b6.

* Update pdo.php

demo/pdo.php

@@ -7,7 +7,7 @@
 
 $pdo = new TraceablePDO(new PDO('sqlite::memory:'));
 $debugbar->addCollector(new PDOCollector($pdo));
-$debugbar['database']->setDurationBackground(true);
+$debugbar['pdo']->setDurationBackground(true);
 
 $pdo->exec('create table users (name varchar)');
 $stmt = $pdo->prepare('insert into users (name) values (?)');