Updates the meta information for a file
$file = $page->file('myimage.jpg');
try {
$file->update(array(
'caption' => 'This is a really nice image',
'year' => 2014
));
echo 'The meta info has been updated';
} catch(Exception $e) {
echo 'The meta info could not be updated';
// optional reason: echo $e->getMessage();
}