Fix flattr url when using https.

Fixes #12.

Signed-off-by: François de Metz <francois@stormz.me>

lib/views/index_logged.jade

@@ -7,7 +7,7 @@ script(type="text/javascript")
       var s = document.createElement('script'), t = document.getElementsByTagName('script')[0];
       s.type = 'text/javascript';
       s.async = true;
-      s.src = 'http://api.flattr.com/js/0.6/load.js?mode=auto';
+      s.src = '//api.flattr.com/js/0.6/load.js?mode=auto';
       t.parentNode.insertBefore(s, t);
   })();