Fix unused 404 handler.
Fix unused 404 handler.

Should proxy to the upstream registry in most cases.

ActiveState/npm-lazy-mirror,ahmednuaman/npm-lazy-mirror,aenario/npm-lazy-mirror,aenario/npm-lazy-mirror,hpcloud/npm-lazy-mirror,ahmednuaman/npm-lazy-mirror,hpcloud/npm-lazy-mirror,ActiveState/npm-lazy-mirror