change flickr api endpoint to use https

the flickr api went ssl-only on june 27th, read more:
http://code.flickr.net/2014/04/30/flickr-api-going-ssl-only-on-june-27th-2014/

I updated my patch to be against the latest develop branch in case that was the reason why https://github.com/oauth-io/oauthd/pull/101 was closed. https://github.com/oauth-io/oauthd/issues/121 is about the same issue.