fixed escape character

trying this:
$brainz->search(new ReleaseFilter(array("release" => "-")));

getting this:
http://musicbrainz.org/ws/2/release/?limit=25&offset=&fmt=json&query=release:/- 400 Bad Request

should be:
http://musicbrainz.org/ws/2/release/?limit=25&offset=&fmt=json&query=release:\- 200 OK