Prefix player_id in Vimeo wrapper to work around bug in current player

Fix for issue https://github.com/mozilla/popcorn-js/issues/417.

An update to the Vimeo player on November 20th, 2014 breaks Popcorn support by ignoring numeric values for player_id when firing events. This fix simply prefixes the ID with a string, causing Vimeo player events to return it properly.