Sample user insert snippet.

The execute_query command to insert users into a sample database doesn't work with postgres due to the use of database specific string escape quotes. Changed to use the doctrine insert command which is less DB specific and better illustrates the use of DBAL.

doc/providers/security.rst

@@ -497,8 +497,17 @@ sample users::
 
         $schema->createTable($users);
 
-        $app['db']->executeQuery('INSERT INTO users (username, password, roles) VALUES ("fabien", "5FZ2Z8QIkA7UTZ4BYkoC+GsReLf569mSKDsfods6LYQ8t+a8EW9oaircfMpmaLbPBh4FOBiiFyLfuZmTSUwzZg==", "ROLE_USER")');
-        $app['db']->executeQuery('INSERT INTO users (username, password, roles) VALUES ("admin", "5FZ2Z8QIkA7UTZ4BYkoC+GsReLf569mSKDsfods6LYQ8t+a8EW9oaircfMpmaLbPBh4FOBiiFyLfuZmTSUwzZg==", "ROLE_ADMIN")');
+        $app['db']->insert('users', array(
+          'username' => 'fabien',
+          'password' => '5FZ2Z8QIkA7UTZ4BYkoC+GsReLf569mSKDsfods6LYQ8t+a8EW9oaircfMpmaLbPBh4FOBiiFyLfuZmTSUwzZg==',
+          'roles' => 'ROLE_USER'
+        ));
+
+        $app['db']->insert('users', array(
+          'username' => 'admin',
+          'password' => '5FZ2Z8QIkA7UTZ4BYkoC+GsReLf569mSKDsfods6LYQ8t+a8EW9oaircfMpmaLbPBh4FOBiiFyLfuZmTSUwzZg==',
+          'roles' => 'ROLE_ADMIN'
+        ));
     }
 
 .. tip::