<?php
/**
 *   Copyright 2013 Vimeo
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 */
ini_set('display_errors', 'On');
error_reporting(E_ALL);

require_once('vendor/autoload.php');

use Vimeo;

$config = json_decode(file_get_contents('./config.json'), true);

$lib = new Vimeo($config['client_id'], $config['client_secret']);
$user = $lib->request('/users/dashron');
print_r($user);

<?php
/**
 *   Copyright 2013 Vimeo
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 */
ini_set('display_errors', 'On');
error_reporting(E_ALL);

require_once('vendor/autoload.php');

$config = json_decode(file_get_contents('./config.json'), true);

$lib = new Vimeo\Vimeo($config['client_id'], $config['client_secret']);
$user = $lib->request('/users/dashron');
print_r($user);

Remove use Vimeo and add Vimeo\Vimeo.
Remove use Vimeo and add Vimeo\Vimeo.