Change getRank date format to fix autocomplete order, fixes #129

This fixes the issue in the autocomplete dropdown box, and also on the search results page.
As far as I can tell https://github.com/camdram/sphinx-realtime-bundle/blob/master/Transformer/ModelToSphinxAutoTransformer.php#L66 is not used in the ranking process.
According to my /etc/sphinx/sphinx.conf sphinx stores this rant as a uint, which would explain the error.