Update Opengraph.php

When running multiple url's after each other, the storage isn't reset; 
    $data = array();
    $reader = new Opengraph\Reader();
    $reader->parse(file_get_contents('http://www.imdb.com/title/tt0117500/'));
    $data[] = $reader->getArrayCopy();
    $reader = new Opengraph\Reader();
    $reader->parse(file_get_contents('http://nu.nl/'));
    $data[] = $reader->getArrayCopy();

When the second URL doesn't have Opengraph data, it shows the data off the first URL.