Added last_seen to authors routing config exclude

refs https://github.com/TryGhost/Toolbox/issues/503

- The "last_seen" property is not used in routing calculations. Without it the routing service was triggering an expensive process on each user login.

ghost/core/core/server/services/url/config.js

@@ -128,7 +128,8 @@ module.exports = [
                 'accessibility',
                 'meta_title',
                 'meta_description',
-                'tour'
+                'tour',
+                'last_seen'
             ],
             filter: 'visibility:public',
             shouldHavePosts: {