Mount the error handler after the routes.
Mount the error handler after the routes.

This catches route errors forwarded to `next`.

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