Fix #359, use better shot URL generation
Fix #359, use better shot URL generation

fzzzy/pageshot,fzzzy/pageshot,mozilla-services/screenshots,mozilla-services/pageshot,mozilla-services/screenshots,mozilla-services/pageshot,mozilla-services/screenshots,fzzzy/pageshot,mozilla-services/screenshots,mozilla-services/pageshot,mozilla-services/pageshot,fzzzy/pageshot